Vacuum chamber made of aluminum or its alloys, and surface treatment and material for the vacuum chamber

ABSTRACT

The present invention relates to a vacuum chamber and chamber parts made of aluminum or its alloys which exhibit excellent corrosion resistance to a corrosive gas or plasma introduced into the vacuum chamber, the surface treatment, and material for the vacuum chamber. The vacuum chamber has a porous layer with a structure in which a pore diameter at the top thereof is small, while a pore diameter at the bottom thereof is large. In order to give such a structure to the porous layer, a final anodizing voltage is set to be higher than an initial anodizing voltage when the surface of the base material is anodized. After the porous-type anodizing is completed, non-porous type anodizing may be conducted so as to grow a barrier layer. Furthermore, the base material made of aluminum alloy preferably has particles such as precipitates and/or deposits with a diameter of 10 μm or less in average, and the precipitates and/or deposits are arranged in parallel with a largest surface of the base material.

This is a 371 of application Ser. No. PCT/JP95/02263, filed Nov. 6,1995.

FIELD OF THE INVENTION

The present invention relates to a vacuum chamber and chamber parts madeof aluminum or its alloys used for a chemical vapor deposition device, aphysical vapor deposition device, a dry etching device, and the like.The vacuum chamber and chamber parts exhibit excellent corrosionresistance to a corrosive gas or plasma introduced into the chamber. Thepresent invention also relates to a surface treatment and material forthe vacuum chamber and chamber parts.

BACKGROUND OF THE INVENTION

A vacuum chamber and chamber parts used for a chemical vapor depositiondevice, a physical vapor deposition device, a dry etching device, andthe like are required to have corrosion resistance to a corrosive gas(hereinafter, referred to as gas corrosion resistance or resistance togas corrosion), because a corrosive gas containing halogen elements suchas chlorine, fluorine, bromine and the like are introduced into thechamber as a reactive gas, an etching gas, and a cleaning gas. Inaddition to the corrosive gas introduction, halogen-based plasma isgenerated in the chamber in many cases. Therefore, the vacuum chamberand chamber parts are also required to have corrosion resistance toplasma (hereinafter, referred to as plasma resistance).

To satisfy such requirements, conventionally, a vacuum chamber has beenmainly made of stainless steel. However, a vacuum chamber made ofstainless steel is heavy in weight, and therefore, requires large-scalefoundation to support its construction. In addition, a vacuum chambermade of stainless steel does not have sufficient thermal conductivity,and therefore, much time is required for baking operation. There is alsoa problem that heavy metal such as chromium and nickel, which are alloycomponents of stainless steel, are released into the atmosphere duringoperation, resulting in spoilage the products treated in the vacuumchamber. Under such circumstances, studies have been conducted todevelop a vacuum chamber and chamber parts made of aluminum or itsalloys which is lighter in weight than those made of stainless steel andis excellent in thermal conductivity without the problem of heavy metalcontamination.

However, without being subjected to surface treatment, a surface ofaluminum or its alloys is not always excellent in resistance to gascorrosion and plasma. To give resistance to gas corrosion and plasma,any surface treatment is necessary. For this purpose, various studieshave been conducted. For example, Japanese Patent Publication No.5-53870 discloses a vacuum chamber which uses aluminum or its alloyswhose surface is anodized to form an anodic oxide coating, therebyincreasing gas corrosion resistance. However, no prior art, includingthe invention disclosed in Japanese Examined Patent Publication No.5-53870, provides an anodic oxide coating which sufficiently serves as aprotective coating against a corrosive gas and plasma. If an anodicoxide coating or a base material is corroded and damaged, products bythe corrosion come out therefrom in a particle form. If a vacuum chamberor chamber part having such a coating layer or a base material is usedin, for example, a semiconductor manufacturing, defective products maybe produced. Accordingly, there has been a demand for improvement.

Japanese Patent publication No. 5-53871 discloses that an ion platingmethod is employed to form a coating (made of, for example, TiN, TiC,and the like) excellent in corrosion resistance on the surface of avacuum chamber made of aluminum or its alloy. However, if the coating isformed by the vapor phase synthesis method such as ion plating, problemsarise in that the obtained coating has small density and high cost isrequired for treatment. Japanese Patent Publication No. 5-53872discloses an ion-implantation method. This method, however, is notadequate for treating a vacuum chamber or chamber part with acomplicated form, and in addition, requires high cost for treatment aswell as an ion plating method.

The present invention has been conducted to solve the above-describedproblems, and the first objective thereof is to provide a vacuum chamberor chamber part made of aluminum or its alloys excellent in resistanceto gas corrosion and plasma by an economical anodizing method.

The second objective of the present invention is to provide a method fortreating a surface the vacuum chamber and chamber parts.

The third objective of the present invention is to provide material usedfor producing the vacuum chamber and chamber parts.

SUMMARY OF THE INVENTION

To achieve the first objective, the present invention is directed to avacuum chamber made of aluminum or its alloys comprising an anodic oxidecoating including a porous layer having a number of pores and a barrierlayer without pores (see FIG. 1 and FIG. 2). Each of pores has anopening on a surface, and its diameter is smaller at the top of theporous layer than at a bottom thereof. The thickness of the barrierlayer is determined in accordance with a pore diameter in the porouslayer which is formed immediately above the barrier layer. A barrierlayer also can be formed by non-porous type anodizing as will bedescribed later.

As described above, a pore diameter is smaller at the top of the porouslayer than at a bottom thereof. The pores in the porous layer may have asection where its diameter continuously or discontinuously changes in adepth direction, or may have a section where its diameter remainsconstant in a depth direction.

When the anodic oxide coating contains two or more elements selectedfrom the group consisting of carbon, sulfur, nitrogen, phosphorus,fluorine and boron, further corrosion resistance can be achieved.

Aluminum or its alloys used for producing a base material of the vacuumchamber or chamber part is produced in such a texture that particlessuch as precipitates and/or deposits contained therein have a diameterof 10 μm or less in average or are arranged in parallel with the largestsurface of the base material. In this order, the base material itselfgains further corrosion resistance as well as the anodic oxide coating.It is preferable that the precipitates and/or deposits have a diameterof 10 μm or less in average and also are arranged in parallel with thelargest surface of the base material.

In the present invention, a vacuum chamber means not only a vacuumchamber itself, but also the vacuum chamber parts partially or entirelymade of aluminum alloy such as gas diffusion plate(GDP), clamper, showerhead, susceptor, clamp ring, electrostatic chuck, and the like.Hereinafter, a vacuum chamber is a general term for a vacuum chamberitself and such parts. The entire vacuum chamber is not necessarily madeof aluminum alloys of the present invention, but may be made incombination with the aluminum alloy of the present invention andaluminum alloy produced by any other method than that of the presentinvention, conventionally known stainless steel, composite material ofceramics and plastics, and the like.

Hereinafter, there are some cases where the above-described vacuumchamber of the present invention is referred to as the first invention.

To achieve the second objective, the present invention is directed to amethod for anodizing the surface of a vacuum chamber made of aluminum orits alloys. When the surface of vacuum chamber is anodized, a finalanodizing voltage is set to be higher than an initial anodizing voltage.

When the final anodizing voltage is set to be higher than the initialanodizing voltage, the anodizing voltage is continuously ordiscontinuously changed for an arbitrary period, or may be kept constantfor an arbitrary period.

The initial anodizing voltage is preferably 50V or less, and the finalanodizing voltage is preferably 30V or more.

It is recommended that a solution containing oxalic acid is used as ananodizing solution, and 1 gram or more of oxalic acid is contained per 1liter of solution. It is more preferable that the anodizing solutioncontains one or more elements selected from the group consisting ofsulfur, nitrogen, phosphorus, fluorine and boron, or contains a compoundincluding such elements.

In the present invention, an initial anodizing voltage indicates anelectrolytic voltage applied when the formation of anodic oxide coatingis substantially started. A final anodizing voltage indicates anelectrolytic voltage applied when the formation of anodic oxide coatingis substantially completed.

Hereinafter, there are some cases where the surface treatment method isreferred to as the second invention.

As described above, to achieve the second objective, the surface of thevacuum chamber made of aluminum or its alloys is anodized so as to forman anodic oxide coating including a porous layer having a number ofpores and a barrier layer without pores, and each of the pores has anopening on the surface. First, the surface of the vacuum chamber issubjected to a porous-type anodizing, and then, is subjected to anon-porous type anodizing. Hereinafter, there are some cases where sucha surface treatment method is referred to as the third invention.

In the present invention, a porous-type anodizing indicates a normalanodizing by which a porous layer and a barrier layer are formed. Theporous layer has a number of pores having an opening on the surface ofthe chamber, and the barrier layer has no pores and is formed on theinterface between the porous layer and the base material. Theporous-type anodizing is conducted by using a solution containingsulfuric acid, phosphoric acid, oxalic acid, chromic acid, or a mixturethereof as an electrolytic solution under the electrolytic voltage inthe range between 5V and 200V.

The non-porous type anodizing indicates an anodizing by which a barrierlayer with no pores is formed. The non-porous type anodizing isconducted by using a boron-base solution (for example, a solutioncontaining a mixture of boron and ammonium borate,), a phosphorus-basesolution (for example, an ammonium dihydrogenphosphate solution), aphthalic acid-base solution (for example, a potassium hydrogenphthalatesolution), an adipic acid-base solution (for example, an ammoniumadipate solution), a carbon-base solution (for example, a sodiumcarbonate solution), a citric acid solution, a tartaric acid solution, asodium chromate solution, or a mixed solution thereof under theelectrolytic voltage in the range between 60V and 500V.

To solve the third objective, the material used for producing the vacuumchamber of the present invention is made of aluminum alloys, and hasprecipitates and/or deposits having a diameter of 10 μm or less inaverage.

Instead of controlling the particle diameter, the precipitates and/ordeposits may be arranged in such a texture as to be in parallel with thelargest surface of the base material.

The material made of aluminum alloy gains further corrosion resistanceby controlling both the particle diameter and the arrangement directionof the precipitates and/or deposits.

It is recommended that the precipitates and/or deposits have avolumetric proportion of 2% or less.

Hereinafter, there are some cases where the material used for the vacuumchamber of the present invention is referred to as the fourth invention.

In the present invention, precipitates indicate compounds generated froma liquid phase during the production of aluminum alloy. Depositsindicate compounds generated from a solid phase during the production ofaluminum alloy. Kinds of precipitates and/or deposits depend on thecomposition of aluminum alloy, and are not limited by the series ofaluminum alloy. Examples of precipitates and deposits are as follows.

Examples of precipitates generated in 1000-series aluminum alloy(hereinafter, 1000-series precipitates) include Al--Fe--seriesprecipitates such as Al₃ Fe, Al₆ Fe and the like, and Al--Fe--Si--seriesprecipitates such as α-AlFeSi, β-AlFeSi and the like.

Examples of precipitates generated in 2000-series alluminum alloy are ofthe identical kinds to 1000-series precipitates. Examples of depositsthereof include Al₂ Cu, Al₂ CuMg, Al₆ CuMg₄ and the like.

Examples of precipitates generated in 3000-series aluminum alloyinclude, in addition to those identical kinds to the 1000-seriesprecipitates, Al₆ Mn, Al₄ Mn, AlMn, Al₁₂ Mn, Al₁₂ Fe₃ Si, Al₁₂ Mn₃ Si,Al₉ Mn₂ S and the like. Deposits thereof is mainly Al₆ Mn.

Examples of precipitates generated in 5000-series aluminum alloyinclude, in addition to those of identical kinds to the 1000-seriesprecipitates, Al₃ Mg₂, Al₁₂ Mg₁₇, Al₇ Cr, Al₁₈ Mg₃ Cr₂, Al₁₈ Mg₃ Mn₂ andthe like. Examples of deposits thereof include Al₃ Mg₂, Al₂ CuMg and thelike.

Examples of precipitates generated in 6000-series aluminum alloyinclude, in addition to those of identical kinds to 1000-seriesprecipitates, Mg₂ Si, Si, Al₈ Mg₅ and the like. Examples of depositsthereof include Mg₂ Si, Al₂ CuMg and the like.

Examples of precipitates generated in 7000-series aluminum alloyinclude, in addition to those of identical kinds to 1000-seriesprecipitates, Al₈ Mg₅, AlZn, Mg₂ Zn₁₁, MgZn₂ and the like. Examples ofdeposits thereof include Mg₂ Zn₁₁, MgZn₂, Al₂ Mg₃ Zn₃, Al₂ CuMg and thelike.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectional view schematically showing a structureof a porous-type anodic oxide coating;

FIG. 2 is a cross-sectional view showing a porous-type anodic oxidecoating;

FIG. 3 is a graph illustrating a relationship between an electrolyticvoltage and a current density in the case of using three kinds ofanodizing solution respectively;

FIG. 4 is a diagram illustrating the patterns of an electrolytic voltageapplied in the surface treatment of the present invention;

FIG. 5 is a diagram illustrating the comparative examples of patterns ofan electrolytic voltage applied in the surface treatment;

FIG. 6 is a diagram illustrating the patterns of an electrolytic voltageapplied in the surface treatment of the present invention;

FIG. 7 is a diagram illustrating the comparative examples of patterns ofan electrolytic voltage applied in the surface treatment;

FIG. 8 is a diagram illustrating a structure of an anodic oxide coatingformed by the surface treatment method of the present invention;

FIG. 9 is a micrograph showing precipitates and/or deposits arranged ina direction perpendicular to the surface of the base material; and

FIG. 10 is a micrograph showing precipitates and/or deposits arranged ina direction parallel to the surface of the base material.

BEST MODE FOR CARRING OUT THE INVENTION

A conventional vacuum chamber and chamber parts made of aluminum or itsalloys has been poor in its corrosion resistance to the aforementionedcorrosive gas and/or plasma. To solve this problem, the presentinventors have conducted hard studies on the techniques for improvingthe surface quality of a vacuum chamber and chamber parts, and havereached the first invention. That is, when a vacuum chamber and chamberparts made of aluminum or its alloys is anodized, it is possible tocontrol the internal structure and the composition of components of itsanodic oxide coating, thereby remarkably enhancing the resistance to gascorrosion and plasma.

In a prior art, it is already known to control the thickness of anodicoxide coating in anodizing (for example, see Japanese Patent PublicationNo. 5-53870). It is also known to change the structure of anodic oxidecoating by changing the conditions of electrolysis. However, there hasbeen no attempt to suppress corrosion caused by a corrosive gas orplasma by controlling the internal structure or the composition ofcomponents of anodic oxide coating. In addition, there has been noreport about studies conducted from such a point of view.

FIG. 1 is a partially sectional view conceptually showing a schematicstructure of an anodic oxide coating which is formed on the surface of avacuum chamber or chamber part made of aluminum or its alloys byanodizing. When electrolysis is started, cells 2 grow in a base material1 in the depth direction. Each of cells 2 has a pore 3 along the lengththereof in the center portion.

FIG. 2 is a cross sectional view of the anodic oxide coating. In thepresent invention, the anodic oxide coating includes a porous layer 4and a barrier layer 5. The porous layer 4 has pores 3, and the barrierlayer 5 has no pores. The barrier layer 5 is interposed between theporous layer 4 and the base material 1. Having no permeability to gas,the barrier layer 5 prevents gas or plasma from coming into contact withthe base material made of aluminum or its alloys.

It has been found that when an anodic oxide coating includes a porouslayer and a barrier layer, there is a correlation among a pore diameterof the porous layer, a cell diameter thereof, and a thickness of thebarrier layer.

The present inventors have studied the relationship between thestructure and the resistance to gas corrosion and plasma of the anodicoxide coating. As a result, the present inventors have reached thefollowing conclusions.

First, the anodic oxide coating exhibits more excellent plasmaresistance as the porous layer has a pore diameter and a cell diametersmaller at the top thereof. The reason thereof is as follows. If thediameter of pores and cells is large at the top, plasma is likely toconcentrate to the peripheries of pores on the surface of the anodicoxide coating. This makes micro-localized plasma condition on thesurface of the anodic oxide coating. Contrary to this, if pores haveopenings with small diameter at the top, the uniformity of the surfaceof the anodic oxide coating is increased, so that the localizedconcentration of plasma can be prevented. In addition, the small porediameter makes it difficult for gas and plasma components to penetrateinto the anodic oxide coating, and to accumulate onto the surface ofporous layer in the form of any compound.

Second, the anodic oxide coating exhibits more excellent resistance togas corrosion as the porous layer has a pore diameter and a celldiameter larger at the bottom thereof. The reason thereof is as follows.If the diameter of pores and cells is large, a substantial surface areaof inside the pore becomes small, so that an area capable of reactingwith corrosive gas becomes small. Consequently, the internal structureof anodic oxide coating is hard to be adversely affected by the changein volume thereof due to reaction products.

Third, an anodic oxide coating exhibits more excellent resistance to gascorrosion as the thickness of barrier layer is larger. The reasonthereof is as follows. As described above, the barrier layer prevents acorrosive gas from coming into contact with the base material made ofaluminum or its alloys. However, there are some corrosive gases whichwill gradually penetrate into the barrier layer when the base materialis left in such a gas atmosphere for a long time. Accordingly, it isdesirable that the barrier layer has a large thickness in order toshield a corrosive gas and also to achieve excellent gas corrosionresistance even when the base material is left in a corrosive gasatmosphere for a long time.

From the above point of view, it is desirable that a porous layer has astructure in which a pore diameter at the top thereof is as small aspossible, while a pore diameter at the bottom thereof is as large aspossible so that a barrier layer has a large thickness.

The present invention does not limit the pore diameter to the specificvalue. In the present invention, at least the pore diameter at thebottom of the porous layer is larger than that at the top thereof,thereby enhancing the corrosion resistance. In order to achieveexcellent plasma resistance, it is desirable that the pore 5 diameter atthe top is 80 nm or less, and more preferably 50 nm or less, and themost preferably 30 nm or less. In order to achieve excellent gascorrosion resistance, it is desirable that a barrier layer has athickness of 50 nm or more, and more preferably 80 nm or more.

Furthermore, in the present invention, it is enough that the porediameter of the porous layer is larger at the bottom thereof than at thetop thereof, and the pore diameter of the intermediate portion betweenthe top and the bottom is not limited to the specific value. Therefore,the intermediate portion may include a section where its pore diametercontinuously changes, a section where its pore diameter discontinuouslychanges, and a section where its pore diameter remains constant. Thesesections may be mixedly present in the intermediate portion. The poremay have a section with a decreased diameter in a way from the bottom tothe top, or the pore may disappear in a way from the bottom to the top.

When a pore diameter continuously changes, there are various changepatterns. For example, a pore diameter gradually increases from the topto the bottom, or may gradually increase from the top toward the baseside, and then, decrease at any point, and after that, increase towardthe bottom again.

In addition, the porous layer can have a multilayered structure, wheretwo or more layers with a pore diameter different from each other areaccumulated, so that the pore diameter of the porous layer graduallychanges. In this case, it is desirable that the differences in the porediameters among these layers are as small as possible, and that thelayer positioned in the middle portion of the porous layer has poreswhose diameter continuously change, so that the pores have taperedsurfaces. The structure of porous layer may be selected depending on theapplication site in the vacuum chamber and chamber parts.

In the above description, the internal structure, specifically a porediameter, of the anodic oxide coating changes in the depth direction. Inthis case, if the electrolysis is conducted while changing itsconditions to change pore diameters, the surface of anodic oxide coatingdoes not always have pores of uniform diameter. In many cases, the porediameter is nonuniform depending on the shape of surface and the areawhere pores are formed. Therefore, the surface areas which requireespecially high plasma resistance can be selectively treated in such amanner as to have a diameter as small as possible. As a result, theremay be some portions which do not satisfy the requirements of thepresent invention, but it is enough that the total structure of theanodic oxide coating satisfies the requirements of the presentinvention.

In some cases, pores are sealed after the completion of anodizing. Thistreatment is referred to as a pore sealing treatment. In the presentinvention, the pore sealing treatment can be conducted as far as it doesnot adversely affect the quality of the anodic oxide coating intended inthe present invention. The pore sealing treatment is useful to achievethe coating performance as has been conventionally reported.Accordingly, as far as the entire structure of the anodic oxide coatingsatisfies the requirements of the present invention, it is possible toachieve the effect intended in the present invention.

In the present invention, the thickness of anodic oxide coating is notlimited to a specific value; however, a preferable thickness to achieveexcellent corrosion resistance is 0.05 μm or more, and more preferably0.1 μm or more. In this case, if the anodic oxide coating has too largethickness, internal force is generated to cause cracks, resulting ininsufficient coating quality or peeling. Therefore, the desirable upperlimit of the thickness is 50 μm. In other words, with a thickness ofmore than 50 μm, it becomes difficult for the anodic oxide coating toreduce internal force by itself. This may cause the anodic oxide coatingto crack and peel off, resulting in generating defective products.

In the present invention, there is no limitation on a kind of solutionused for electrolysis. The solution may contain, for example, aninorganic acid such as sulfuric acid, phosphoric acid, chromic acid, oran organic acid such as formic acid and oxalic acid. It is recommended,however, to use solution containing 1 gram or more of oxalic acid per 1liter of the solution, because the use of such a solution enables theelectrolytic voltage in anodizing to be arbitrarily controlled in abroad range. FIG. 3 is a graph illustrating a relationship between theelectrolytic voltage and the current density when an anodic oxidecoating is formed under various electrolytic conditions using threekinds of anodizing solutions containing sulfuric acid, oxalic acid, andphosphoric acid, respectively. With a sulfuric acid solution, an anodicoxide coating is formed at a high rate, because the current densitygreatly changes when the electrolytic voltage is changed. With aphosphoric acid solution, an anodic oxide coating is formed at a lowrate, because the current density slowly changes even though theelectrolytic voltage is greatly changed. From this result, it can besaid that when a sulfuric acid solution is used, an anodic oxide coatingis formed at too high rate to control the coating thickness. On theother hand, when a phosphoric acid solution is used, an anodic oxidecoating is formed at too low rate, resulting in poor productionefficiency. Contrary to this, when an oxalic acid solution is used, thechange in current density with respect to the electrolytic voltage is inthe middle value between that using a sulfuric acid solution and thatusing a phosphoric acid solution. In addition, when using an oxalic acidsolution, the structure of anodic oxide coating can be easily controlledwith less deterioration of production efficiency than the case of usinga phosphoric acid solution.

As described above, an anodic oxide coating obtains high resistance togas corrosion and plasma by controlling the structure thereof. Thepresent inventors have conducted further studies, and have found thatfurther improvement in corrosion resistance can be achieved by adjustinga composition of components of anodic oxide coating. More specifically,an anodic oxide coating gains further resistance to gas corrosion andplasma when it contains two or more elements selected from the groupconsisting of carbon, sulfur, nitrogen, phosphorus, fluorine, and boron(hereinafter, referred to as present elements in some cases.).

When an anodizing solution contains an organic acid such as oxalic acidand formic acid, the produced anodic oxide coating contains acarbon-containing compound such as HCOOH and (COOH)₂ (or a compoundcontaining C_(x) O_(y) H_(z) groups such as --CO₃,--C₂ O₄, and --COOH,where x, y, and z are integers satisfying the conditions of x≧1, and yand z≧0). Accordingly, when an organic acid solution such as oxalic acidsolution is used in anodizing, one or more elements other than carbon,selected from the group consisting of sulfur, nitrogen, phosphorus andboron, is added thereto, so that the anodic oxide coating contains twoor more elements. Below-described are examples of compounds to be addedto the anodizing solution.

(1) In the Case where Sulfur is Added to an Anodizing Solution

An element such as H₂ SO₄, Al₂ (SO₄)₃ and the like is added to ananodizing solution, so that the produced anodic oxide coating contains asulfur-containing compound such as H₂ SO₄, H₂ SO₃, Al₂ (SO₄)₃, Al(HSO₄)₃and the like (or a compound containing S_(x) O_(y) H_(z) groups such as--SO₄, --SO₃, --HSO₄ and the like, where x, y, and z are integerssatisfying the conditions of x≧1, and y and z>0).

(2) In the Case where Nitrogen is Added to an Anodizing Solution

An element such as HNO₃, Al(NO₃)₃ and the like is added to an anodizingsolution, so that the produced anodic oxide coating containsnitrogen-containing compound such as HNO₃, HNO₂, Al(NO₃)₃ and the like(or a compound containing N_(x) O_(y) H_(z) groups such as --NO₃, --NO₂and the like, where x, y, and z are integers satisfying the conditionsof x≧1, and y and z≧0).

(3) In the Case where Phosphorus is Added to an Anodizing Solution

An element such as H₃ PO₄, H₃ PO₃, AlPO₄ and the like is added to ananodizing solution, so that the produced anodic oxide coating containsphosphorus-containing compound such as H₃ PO₄, H₂ PHO₃, AlPO₄ and thelike (or a compound containing P_(x) O_(y) H_(z) groups such as --PO₄,--HPO₄, --H₂ PO₄, --HPHO₃ and the like, where x, y, and z are integerssatisfying the conditions of x≧1, and y and z≧0).

(4) In the Case where Fluorine is Added to an Anodizing Solution

An element such as hydrogen fluoride is added to an anodizing solution,so that the produced anodic oxide coating contains fluorine-containingcompound.

(5) In the Case where Boron is Added to an Anodizing Solution

An element such as (NH₄)₂ B₄ O₇, H₃ BO₃ and the like is added to ananodizing solution, so that the produced anodic oxide coating containsboron-containing compound such as B₂ O₃, (NH₄)₂ B₄ O₇ and the like (or acompound containing B_(x) O_(y) H_(z) groups such as --BO₃, --B₄ O₇ andthe like, where x, y, and z are integers satisfying the conditions ofx≧1, and y and z≧0).

The compound is added to the anodizing solution in the amount of 0.1gram or more per 1 liter of the solution upon being converted into theamount of each element, i.e., sulfur, nitrogen, phosphorus, fluorine andboron. With the amount of less than 0.1 gram per 1 liter, it isdifficult to achieve remarkable effect.

As already described, when an oxalic acid solution is used as ananodizing solution, the produced anodic oxide coating containscarbon-containing compound derived from the oxalic acid. Therefore, itis enough that one or more present elements other than carbon (i.e.,sulfur, nitrogen, phosphorus, fluorine and boron) is added to theanodizing solution. When a sulfuric acid solution is used as ananodizing solution, the produced anodic oxide coating containssulfur-containing compound derived from the sulfuric acid. Therefore, itis enough that one or more present elements other than sulfur (i.e.,carbon, nitrogen, phosphorus, fluorine and boron) is added to theanodizing solution. Depending on the element originally contained in theanodizing solution, a compound containing one or more other presentelements is added to the anodizing solution. As a result, the producedanodic oxide coating can contain two or more present elements.

Besides the method in which the above-described compound is added to theanodizing solution, it is possible to employ other methods for allowingtwo or more present elements to be contained in the anodic oxidecoating. For example, it is possible to use the base material made ofaluminum alloy containing the present elements as an alloying element.It is also possible to allow the present elements to be contained onlyin the surface layer of the base material by a surface reforming methodsuch as ion implantation, which is then subjected to anodizing. In anyof these methods, the produced anodic oxide coating contains two or morepresent elements, thereby gaining the enhanced resistance to gascorrosion and plasma.

In order to enhance the resistance to gas corrosion and plasma, thepreferable amount (in the unit of weight %) of the present elements tobe contained in the anodic oxide coating is as follows. In the case ofcarbon, the preferable amount is 0.01% or more, and more preferably 0.5%or more. In the case of sulfur, the preferable amount is 0.02% or more,and more preferably 2% or more. In the case of nitrogen, the preferableamount is 0.01% or more, and more preferably 0.7% or more. In the caseof phosphorus, the preferable amount is 0.015%, and more preferably 1%or more. In the case of fluorine, the preferable amount is 0.01%, andmore preferably 0.5% or more. In the case of boron, the preferableamount is 0.015%, and more preferably 0.3% or more.

In the present invention, an aluminum alloy used for a base material isnot limited to a specific kind. However, it is desirable that the vacuumchamber is made of 1000-series alloy, 5000-series alloy, and 6000-seriesalloy due to their excellent mechanical strength, thermal conductivity,electric conductivity, and corrosion resistance. A 1000-series alloy isa high purity aluminum-series alloy. A 5000-series alloy is desired tocontain at least 0.5 or less weight % of silicon and 0.5 to 6.0 weight %of magnesium as alloy contents. A 6000-series alloy is desired tocontain at least 0.2 to 1.2 weight % of silicon and 0.4 to 1.5 weight %of magnesium as alloy contents. The components of the chamber may bemade of 2000-series alloy and 7000-series alloy besides 5000-seriesalloy and 6000-series alloy. It is known that the use of aluminum alloycontaining magnesium, silicon, copper, iron and the like as alloycontents enhances the resistance to cracks of the anodic oxide coatinggenerated by high frequency and high temperature (heat cycle), andreduces internal force inside the anodic oxide coating. Especially, a6000-series alloy has a high performance when including magnesium andsilicon as alloy contents, and the performance can be further increasedby conducting thermal treatment at the final step of the productionthereof.

Next, the second invention will be described.

In the second invention, the surface of the base material made ofaluminum alloy is anodized under the condition where a final anodizingvoltage is higher than an initial anodizing voltage. In this order, ananodic oxide coating is formed with an internal structure which providesexcellent resistance to both the gas corrosion and plasma.

In order to suppress the reaction with plasma, the porous layer isrequired to have a smooth surface with a small pore diameter and a smallcell diameter. In the formation of anodic oxide coating, the anodizingproceeds starting from the surface of the base material along the depthdirection, and the bottom end structure is dependent on the anodizingvoltage. Once the formation of the anodic oxide coating is completed,the pore diameter and the cell diameter thereof never change even by theapplication of anodizing voltage. As a result, it is preferable that theinitial anodizing voltage is set at low level, and specifically, at 50Vor less, and more preferably at 30V or less. On the other hand, in orderto reduce the internal force inside the anodic oxide coating and toprevent the anodic oxide coating from cracking and peeling off, thebottom end structure of the porous layer is required to have a largepore diameter and large cell diameter. Further, more excellent gascorrosion resistance can be achieved if the anodic oxide coating has abarrier layer with large thickness at the interface between the porouslayer and the base material. Taking these points into consideration, afinal anodizing voltage is required to be higher than an initialanodizing voltage. It is preferable that the final anodizing voltage isset at 30V or more, and more preferably 50V or more, and the mostpreferably 70V or more.

When the final anodizing voltage is higher than the initial anodizingvoltage, the anodizing voltage may be continuously changed in the entireanodizing process, or may be changed stepwise. Specifically, theanodizing voltage may be continuously or discontinuously changed for anarbitrary period in the anodizing process, or may be kept constant foran arbitrary period in the anodizing process.

As described above, an anodizing voltage is changed for a specificperiod in the anodizing process so that an anodic oxide coating isformed with a changing internal structure. Thus-formed structure iseffective of reducing the internal force and the volumetric change ofthe anodic oxide coating resulted from the contact with gas or plasmaduring the use of the vacuum chamber. As a result, it is possible toprevent the anodic oxide coating from cracking or peeling off, which mayotherwise cause corrosion and damage, thereby enhancing the resistanceto gas and plasma.

FIG. 4 is a diagram illustrating voltage patterns when an electrolyticvoltage is continuously changed. As seen in FIG. 4, a voltage level maybe gradually increased starting from the initiation of electrolysis, ora voltage level may be increased to a certain level and then decreased,and again increased. FIG. 4 illustrates the patterns when anelectrolytic voltage is linearly changed; however, an electrolyticvoltage may be curvedly changed.

FIG. 6 is a diagram illustrating patterns when an electrolytic voltageis changed stepwise. As seen in FIG. 6, an electrolytic voltage may beintermittently increased, or may be increased continuously, or may bedecreased once and then again increased. When the electrolytic voltageis changed stepwise, it is recommended that the increase and decrease inthe voltage values are continuous or small. In this manner, an anodicoxide coating has a structure with continuity in the depth direction,thereby avoiding the formation of portions to which the internal forceeasily concentrates.

Next, the third invention will be described. The present inventors havefound that, in order to form an anodic oxide coating excellent in theresistance to both gas corrosion and plasma, in addition to give achanging structure to the porous-type anodic oxide coating, the poroustype anodizing and the non-porous type anodizing are performed to form abarrier layer with a thickness as large as possible.

As shown in FIG. 8, the base material 1 of the vacuum chamber andchamber parts made of aluminum or its alloys is subjected to theporous-type anodizing so as to form the porous layer 4 and the barrierlayer 5. Then, the non-porous type anodizing is performed thereto sothat the barrier layer 6 grows. As a result, the vacuum chamber orchamber part is excellent in the resistance to both gas corrosion andplasma.

As described above, the porous type anodizing may be conducted using asolution containing any one of sulfuric acid, phosphoric acid, oxalicacid and chromic acid, or a mixture thereof under the electrolyticvoltage in the range between 5V and 200V. On the other hand, thenon-porous type anodizing for forming a barrier layer with no pores maybe conducted using a boric acid-base solution, a phosphoric acid-basesolution, a phthalic acid-base solution, an adipic acid-base solution, acarbonic acid-base solution, a citric acid-base solution, a tartaricacid-base solution, and a sodium chromate-base solution, or a mixturethereof under the electrolytic voltage in the range between 60V and500V.

In the present invention, the porous-type anodizing may be conductedunder the electrolytic voltage at a constant value; however, it isrecommended that a final anodizing voltage is higher than an initialanodizing voltage so that the pore diameter at the top of porous layerbecomes larger than at the bottom thereof. The reason thereof is asfollows. In order to achieve excellent plasma resistance, it ispreferable that the porous layer has pores with small diameter at thetop thereof, while in order to achieve excellent gas corrosionresistance, it is preferable that the porous layer has pores and cellswith large diameter at the bottom thereof. More specifically, theinitial anodizing voltage is preferably set at 50V or less, and morepreferably 30V or less. On the other hand, the final anodizing voltageis preferably higher than the initial anodizing voltage, and thespecific value thereof is 30V or more, and more preferably 50V or more,and the most preferably 70V or more.

When the final anodizing voltage is higher than the initial anodizingvoltage in porous-type anodizing, the voltage may be continuouslychanged in the entire anodizing process, or may be changed stepwise.More specifically, the voltage may be continuously or discontinuouslychanged for an arbitrary period in the entire anodizing process, or maybe changed for an arbitrary period while being kept constant for theother arbitrary period.

As described above, in the formation of the porous-type anodic oxidecoating, the anodizing voltage is changed for an arbitrary period in theanodizing process so that the produced anodic oxide coating has achanging internal structure. This structure reduces the internal forceor the volumetric change of the anodic oxide coating due to the contactwith gas or plasma during the use of vacuum chamber. As a result, it ispossible to prevent the anodic oxide coating from cracking or peelingoff, which may otherwise cause corrosion and damage, thereby enhancingthe resistance to gas and plasma.

An anodizing voltage may be continuously changed. In this case, forexample, the voltage may be gradually increased starting from theinitiation of electrolysis, or may be increased to a certain level andthen decreased, and reincreased. FIG. 6 is a diagram showing voltagepatterns when the electrolytic voltage is changed stepwise. As shown inFIG. 6, there are several methods for changing the electrolytic voltage.Patterns A and C show the case where the electrolytic voltage isintermittently increased. Patterns B and C show the case where theincrease in the voltage level is continuous. Patterns E and F show thecase where the electrolytic voltage is increased and then decreased, andreincreased. When an electrolytic voltage is changed stepwise, it isrecommended that the increase and decrease in the voltage are continuousor small. In this manner, the anodic oxide coating is provided with astructure having continuity in the depth direction, thereby avoiding theformation of portions to which the internal force is easilyconcentrated.

In the present invention, a pore diameter of the porous-type anodicoxide coating is not limited to a specific value; however, a porediameter at the bottom is larger than that at the top. With thisstructure, the corrosion resistance is enhanced. In order to achieveexcellent plasma resistance, it is preferable that a pore diameter atthe top is 80 nm or less, and more preferably 50 nm or less, and themost preferably 30 nm or less.

In the present invention, the thickness of the porous layer is notlimited to a specific value; however, in order to achieve excellentcorrosion resistance, it is preferable that the thickness of the porouslayer is 0.05 μm or more, and more preferably 0.1 μm or more. Thedesirable maximum thickness is 50 μm, because if the thickness is toolarge, the porous layer may have cracks due to the internal force. Thismay cause problems such as insufficient coating performance or peelingof the anodic oxide coating. More specifically, if the porous layer hasa thickness of larger than 50 μm, it may be difficult for the anodicoxide coating to reduce its internal force by itself. In this case, theanodic oxide coating may have cracks and peel off, causing a problem ofproducing defective products.

Further, in order to achieve excellent gas corrosion resistance, it ispreferable that the barrier layer has a thickness of 50 nm or more, andmore preferably 80 nm or more.

Next, the fourth invention will be described.

Even though the above-described surface treatment is conducted in theformation of anodic oxide coating, it is impossible to completely avoidthe penetration of corrosive elements into a base material. During theuse of a vacuum chamber or chamber part, corrosive elements passes,though very slowly, through an anodic oxide coating and penetrate into abase material made of aluminum alloy. Therefore, in addition to theimprovement of surface treatment technique, it is also important toenhance the corrosion resistance of material itself used for a vacuumchamber and chamber parts.

Depending on desired physical properties, an aluminum alloy is providedwith several kinds of alloying elements, and at least iron and siliconare always contained as inevitable impurities. A 1000-series alloy,which is not positively provided with alloying elements, also maycontain a certain amount of iron and silicon as inevitable impurities.Accordingly, when using a 1000-series aluminum alloy, the base materialcontains at least 1000-type precipitates which have been alreadydescribed. Duralumin made of 2000-series alloy has the high strengthresulted from the dispersion curing effect of deposits. Accordingly, avacuum chamber made of aluminum alloy contains precipitates such asprecipitates or deposits containing inevitable impurities, alloyingelements and the like.

However, the presence of the precipitates and/or deposits seriouslyimpairs the corrosion resistance, and therefore, is not desirable. Morespecifically, halogen elements such as chlorine, fluorine and brominehave high corrosivity and penetrate into a base material made ofaluminum, causing corrosion of the base material. When a base materialcontains precipitates and/or deposits, halogen elements are likely topenetrate into the interface between the precipitates and/or depositsand the base material made of aluminum. In order to ensure corrosionresistance, it is desirable that a base material contains precipitatesand/or deposits in an amount as small as possible. However, in order toreduce the content of inevitable impurities such as iron and silicon tothe level as low as possible, it is necessary to prepare an aluminumalloy having extremely high purity. This requires high cost and thus isnot practical.

The present inventors have conducted studies to enhance the corrosionresistance of base material made of aluminum alloy on the assumptionthat precipitates and/or deposits are present therein. As a result, ithas been found that when precipitates and/or deposits are present in aminute and uniform state, or are arranged in parallel with the largestarea of the base material, the base material is excellent in corrosionresistance. More specifically, the precipitates and/or deposits arearranged not to be present continuously with respect to the directionalong which the corrosive elements penetrate. With this arrangement, thebase material has the high resistance to both gas corrosion and plasma.

In order to achieve excellent resistance to corrosion, it is effectivethat the precipitates and/or deposits have a diameter of 10 μm inaverage. With a small diameter, precipitates and/or deposits losecontinuity and easily keep adequate spaces each other. As a result, thecorrosion resistance is enhanced. The preferable average diameter ofprecipitates is 6 μm or less, and more preferably 3 μm or less. Thepreferable average diameter of deposits is 2 μm or less in average, andmore preferably 1 μm or less. In this case, if some particles have toolarge diameter even though the average diameter falls within theseranges, the corrosion resistance may be adversely affected. Accordingly,the maximum diameter of the precipitates and/or deposits is preferably15 μm or less, and more preferably 10 μm or less.

In some environment where a vacuum chamber or chamber part is used,deposits may grow and gain their diameters during use. In spite of sucha situation, the maximum diameter thereof preferably falls within theabove-described ranges. However, in the case where a vacuum chamber isused in the environment that does not allow the particle diameter tostay within these ranges, it is desirable to select a base materialhaving deposits with a diameter as small as possible (specifically, abase material having deposits with an average diameter of 2 μm or less,and more preferably 1 μm or less).

In order to disperse precipitates and/or deposits in a minute form in analuminum alloy, a content of alloying element and inevitable impuritiesin an alloy composition is reduced to the level as low as possible.Besides this method, there is also a method in which a casting rate iscontrolled. More specifically, in casting, a cooling rate is increasedto the level as high as possible, thereby controlling the averagediameter and the volumetric proportion of the precipitates and depositsto small values. The cooling rate in casting is preferably 1° C./sec ormore, and more preferably 10° C./sec or more.

The particle diameter, the shape, and the distribution state of thedeposits can be controlled by performing thermal treatment at the finalstep of producing the base material (for example, T4, T6). Specifically,the liquefaction is performed at a temperature as high as possible (forexample, the temperature is increased to the level immediately beforethe solidification is started.) so as to form a supersaturated solidsolution, and after that, multistage aging treatment such as a doublestage treatment and a triple stage treatment is performed. As describedabove, even after the casting, the diameter of deposits can be furtherdecreased by performing the above-described thermal treatment.

Moreover, in hot extrusion or hot rolling performed after the casting,the precipitates and/or deposits are likely to be arranged along thedirections of extrusion and rolling. Even when the aluminum alloycontaining the precipitates and/or deposits arranged along a specificdirection is used for the base material, depending on the shape of eachvacuum chamber, the largest area of the base material is made to beparallel with the arrangement direction thereof, thereby enhancing thecorrosion resistance.

FIG. 9 and FIG. 10 are micrographs showing precipitates and/or depositsviewed from the cross-section of the vacuum chamber. White-coloredportions are precipitates and black-colored portions are deposits. Inboth FIG. 9 and FIG. 10, the upper side is the surface of the vacuumchamber where an anodic oxide coating is formed. In FIG. 9, theprecipitates and/or the deposits are arranged in perpendicular to thesurface of the vacuum chamber. In FIG. 10, the precipitates and/ordeposits are arranged in parallel with the surface of the vacuumchamber. In FIG. 9, there are some precipitates and/or deposits having adiameter of more than 15 μm, while in FIG. 10, all the precipitatesand/or deposits have a diameter of 10 μm or less. Accordingly, FIG. 10illustrates a vacuum chamber with a base material having precipitatesand/or deposits with a diameter of 10 μm or less, and the precipitatesand/or deposits are arranged in parallel with the largest surface of thebase material.

Some kinds of vacuum chamber or chamber part may contain, due to therestriction from their shapes, precipitates and/or deposits arranged inperpendicular with the largest area of the base material. Examples ofsuch vacuum chambers include susceptors, gas diffusion plates,dielectric plates such as electrostatic chucks, all of which have adisk-shaped base material. For example, in many cases, susceptors areproduced in a disk-like shape by cutting a column-like extruded materialinto round slices. Thus-produced susceptors contain precipitates and/ordeposits arranged along a direction of hot extrusion, and thisarrangement direction may be in perpendicular to the surface and bottomof susceptor. Accordingly, when a vacuum chamber is a susceptor likethis, the corrosion resistance is enhanced by controlling the averagediameter of precipitates and/or deposits to be as small as possible,instead of controlling the arrangement direction thereof.

Moreover, the corrosion resistance can be further enhanced by, besidescontrolling the average diameter and/or the arrangement of precipitatesand/or deposits, controlling the volumetric proportion thereof to be assmall as possible. More specifically, the volumetric proportion of theprecipitates and/or deposits is preferably 4% or less, and morepreferably 2% or less, and the most preferably 1% or less.

A preferable combination of the average diameter and the volumetricproportion of the precipitates and/or deposits is as follows. As to theprecipitates, it is preferable that the average diameter is 6 μm or lessand the volumetric proportion is 4% or less (desirably 2% or less), andmore preferably, the average diameter is 3 μm or less and the volumetricproportion is 2% or less (desirably 1% or less). As to the deposits, itis preferable that the average diameter is 2 μm or less and thevolumetric proportion is 4% or less (desirably 2% or less), and morepreferably the average diameter is 1 μm or less and the volumetricproportion is 2% or less (desirably 1% or less).

In some methods and conditions for producing an aluminum alloy, it ispossible to control the diameter and the volumetric proportion of theprecipitates and/or deposits present on the surface of the aluminumalloy. For example, there is a method in which, when solidified, thesurface of an aluminum alloy is rapidly cooled to control the formationof the precipitates and/or deposits. In this case, a pressure may beapplied so that precipitation and deposition are promoted in the bulkmiddle portion of the aluminum alloy. There is also a method in which analuminum alloy excellent in corrosion resistance is cladded on thesurface of the vacuum chamber.

In the above-described methods, control is conducted in such a mannerthat at least the largest area of the base material from the surface upto 1 mm deep contains precipitates having an average diameter of 3 μm orless and a volumetric proportion of 1% or less and deposits having anaverage diameter of 1 μm or less and a volumetric proportion of 1% orless. Consequently, the surface of the base material gains furtherresistance to gas corrosion and plasma, resulting in further enhancingthe corrosion resistance of the entire vacuum chamber.

When a vacuum chamber is produced by using the material of the presentinvention, the corrosion resistance and the abrasion resistance can befurther enhanced by forming a coating on the surface thereof employing aknown surface treatment other than the anodizing. Examples of suchsurface treatments include a physical vapor deposition such assputtering and ion-plating, chemical vapor deposition, and thermalspraying.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention, theyshould be construed as being included therein.

EXAMPLE 1

As shown in Table 1, various aluminum alloy plates were provided with ananodic oxide coating having different structure from each other. Thesealuminum alloy plates were used as test pieces. Each anodic oxidecoating included a porous layer having pores with a diametercontinuously changing in a depth direction. Table 1 also shows thenumber of layers included in each porous layer, a pore diameter at a topand a bottom of each porous layer, an electrolytic solution used foranodizing, and the thickness of each anodic oxide coating.

In order to evaluate the corrosion resistance to a halogen-containinggas for the test pieces, a gas corrosion test was conducted by using 5%of mixed gas of Cl₂ and Ar at a temperature of 300° C. for 4 hours. Uponcompletion of the test, the appearance of test pieces was evaluatedunder the following standards.

<Gas Corrosion Test>

∘: No corrosion was generated.

Δ: Corrosion was generated in an area of less than 5% of test piece.

x: Corrosion was generated in an area of 5% or more of test piece.

In addition, in order to evaluate the resistance to plasma for the testpieces, a chlorine plasma irradiation test was conducted under the lowbias for 90 minutes. Upon completion of the test, the etched depth ofthe test pieces was measured and evaluated under the followingstandards.

<Plasma Irradiation Test>

∘: Test piece was etched in a depth of less than 2 μm.

Δ: Test piece was etched in a depth in the range between 2 μm or moreand less than 5 μm.

x: Test piece was etched in a depth of 5 μm or more.

The results of the gas corrosion test and the plasma irradiation testare shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                   Structure*                                                                              Thickness of                                                                        Gas  Plasma                                       Kind of- of porous Treatment anodic oxide Corrosion irradiation                                                 No. Al alloy layer method coating                                            (μm) test test                         __________________________________________________________________________    Example of                                                                           1 1000-series                                                                         a    anodizing                                                                          2     ∘                                                                      ∘                               present 2 6000-series b  35 ∘ ∘                       invention 3  c  25 ∘ ∘                                 4 5000-series d  0.8 ∘ ∘                              5  e  15 ∘ ∘                                         Comparative 6  f  0.04 x x                                                    example 7 6000-series g  45 x Δ                                          8  h  70 x ∘                                                      9  -- -- -- x x                                                            __________________________________________________________________________

a: top: 10˜200 nm: base (phosphoric acid)

b: top: 15˜20 nm: base (sulfuric acid-oxalic acid)

c: top: 12 ˜55˜30˜120 nm: base (phosphoric acid)

d: top: 8˜250 nm: bottom (phosphoric acid)

e: top: 25˜35 nm: bottom (sulfuric acid-oxalic acid)

f: top: 20˜20 nm: bottom (phosphoric acid)

g: top: 15˜15 nm: bottom (sulfuric acid)

h: top: 5˜10 nm: bottom (sulfuric acid)

As is obvious from the results shown in Table 1, the test pieces Nos. 1to 5, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 6 to 9, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 2

As shown in Table 2, various aluminum alloy plates were provided with ananodic oxide coating having different structure from each other. InExample 2, an oxalic acid solution was used as an electrolytic solution.These aluminum alloy plates were used as test pieces. Each anodic oxidecoating included a porous layer having pores with a diametercontinuously changing in a depth direction. Table 2 also shows thenumber of layers included in each porous layer, a pore diameter at a topand a bottom of each porous layer, and the thickness of each anodicoxide coating.

Repeating the gas corrosion test and the plasma irradiation testconducted in Example 1, the test pieces were tested to evaluate theirresistance to gas corrosion and plasma. The test results are as shown inTable 2.

                                      TABLE 2                                     __________________________________________________________________________                   Structure*                                                                              Thickness of                                                                        Gas  Plasma                                       Kind of- of porous Treatment anodic oxide corrosion irradiation                                                 No. Al alloy layer method coating                                            (μm) test test                         __________________________________________________________________________    Example of                                                                           1 5000-series                                                                         a    oxalic                                                                             15    ∘                                                                      ∘                               present 2  b acid 0.1 ∘ ∘                             invention 3 1000-series c anodizing 5 ∘ ∘                                                 4 6000-series d  35 ∘                                           ∘                                5  e  15 ∘ ∘                                         Comparative 6  f  0.03 x x                                                    example 7  g  40 x Δ                                                     8 1000-series h  60 x ∘                                           9 5000-series -- -- -- x x                                                 __________________________________________________________________________

a: top: 15˜140 nm: bottom

b: top: 20˜150 nm: bottom

c: top: 20˜50˜30˜150 nm: bottom

d: top: 10˜180 nm: bottom

e: top: 10˜20˜10˜70 nm: bottom

f: top: 10˜45 nm: bottom

g: top: 20˜20 nm: bottom

h: top: 5˜40 nm: bottom

As is obvious from the results shown in Table 2, the test pieces Nos. 1to 5, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 6 to 9, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 3

As shown in Table 3, various aluminum alloy plates were provided with ananodic oxide coating having different structure from each other. Thesealuminum alloy plates were used as test pieces. A porous layer includingtwo or more layers had pores with a diameter which changed stepwise.However, the test piece No. 4 had an intermediate layer of which porediameter continuously changed, thereby pores have tapered surfaces.Table 3 also shows kinds of electrolytic solutions used in anodizing andthe thickness of each anodic oxide coating.

Repeating the gas corrosion test and the plasma irradiation testconducted in Example 1, the test pieces were tested to evaluate theirresistance to gas corrosion and plasma. The test results are shown inTable 3.

                                      TABLE 3                                     __________________________________________________________________________                  Structure of porous layer                                                                            Thickness of                                                                        Gas  Plasma                                Kind of                                                                             Number of                                                                          Pore diameter (nm)*                                                                        Treatment                                                                          anodic oxide                                                                        corrosion                                                                          irradiation                     No. Al alloy layers top/bottom method coating (μm) test test             __________________________________________________________________________    Example                                                                             1 1000-series                                                                         2    20(P)/100(P) anodizing                                                                          4     ∘                                                                      ∘                   of 2  3 50(P)/30(S)/70(P)  0.5 ∘ ∘                    present 3 6000-series 2 10(S-0)/120(P)  5 ∘ ∘                                                        invention 4  2 15(S)/tape                                                    red layer (P)/130(P)  30                                                      ∘ .smallcircle                                                    .                                5  3 15(S)/40(P)/150(P)  30 ∘ ∘                       6  5 30(P)/50(P)/80(P)/200(P)  45 ∘ ∘                 7 5000-series 6 20(S)/120(P)/20(S)/120  10 ∘ ∘           (P)/20(S)/180(P)                                                           8  2 80(P)/250(P)  0.2 ∘ ∘                           Comparative 9  1 10(S)  30 Δ Δ                                    example 10 6000-series -- -- -- -- x x                                         11 1000-series 2 10(S)/50(P) anodizing 0.03 x x                               12  2 80(P)/15(S)  70 x Δ                                            __________________________________________________________________________

(P): phosphoric acid anodizing

(S): sulfuric acid anodizing

(S-O): sulfuric acid-oxalic acid anodizing

As is obvious from the results shown in Table 3, the test pieces Nos. 1to 8, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 9 to 12, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 4

As shown in Table 4, various aluminum alloy plates were provided with ananodic oxide coating having different structure from each other. InExample 4, an oxalic acid solution was used as an electrolytic solution.These aluminum alloy plates were used as test pieces. A porous layerincluding two or more layers had pores with a diameter which changedstepwise. However, the test pieces Nos. 2 and 8 had an intermediatelayer of which pore diameter continuously changed, thereby pores havetapered surfaces. Table 4 also shows the structure of each porous layerand the thickness of each anodic oxide coating.

The test pieces were tested to evaluate their resistance to gascorrosion and plasma repeating the gas corrosion test and the plasmairradiation test conducted in Example 1, except that the gas corrosiontest was conduted at 300° C. for 4 hours and the chlorine plasmairradiation test was conducted for 120 minutes. The test results areshown in Table 4.

                                      TABLE 4                                     __________________________________________________________________________                    Structure of porous layer                                                                        Thickness of                                                                        Gas  Plasma                                          Number of                                                                          Pore diameter (nm)                                                                     Treatment                                                                          anodic oxide                                                                        corrosion                                                                          irradiation                       No. Kind of Al alloy layers top/bottom method coating (μm) test          __________________________________________________________________________                                                  test                            Example of                                                                          1 5000-series                                                                           2    10/80    oxalic                                                                             15    ∘                                                                      ∘                     present 2  2 15/tapered acid 35 ∘ ∘                   invention    layer/110 anodizing                                               3  3 20/30/150  0.8 ∘ ∘                               4  4 15/120/30/150  30 ∘ ∘                            5 1000-series 3 15/40/150  20 ∘ ∘                     6  2 40/80  4 ∘ ∘                                     7 6000-series 2 10/150  35 ∘ ∘                        8  2 20/tapered  30 ∘ ∘                                  layer/125                                                                  9  3 15/80/150  25 ∘ ∘                               Comparative 10  1 15  10 x ∘                                      example 11  2 10/220  0.03 Δ x                                           12 1000-series 1 20/50  60 x Δ                                          13 5000-series 3 10/50/100  60 Δ Δ                                14  -- -- -- -- x x                                                        __________________________________________________________________________

As is obvious from the results shown in Table 4, the test pieces Nos. 1to 9, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 10 to 14, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 5

As shown in Table 5, various aluminum alloy plates were provided with ananodic oxide coating having different structure form each other. Thesealuminum alloy plates were used as test pieces. Table 5 also shows thechange in the structure of each porous layer by means of a porediameter, kinds of electrolytic solutions used in anodizing, and thethickness of each anodic oxide coating.

Repeating the gas corrosion test and the plasma irradiation testconducted in Example 1, the test pieces were tested to evaluate theirresistance to gas corrosion and plasma. The test results are shown inTable 5.

                                      TABLE 5                                     __________________________________________________________________________                  Structure of                                                      porous layer  Thickness of Gas Plasma                                               Kind of                                                                             Numbers of                                                                          Pore Treatment                                                                          anodic oxide                                                                        corrosion                                                                          irradiation                            No. Al alloy layer diameter method coating (μm test test                 __________________________________________________________________________    Example of                                                                          1 5000-series                                                                         2     a    anodizing                                                                          15    ∘                                                                      ∘                          present 2  3 b  0.08 ∘ ∘                              invention 3 6000-series 2 c  35 ∘ ∘                    4  4 d  2 ∘ ∘                                         5  5 e  45 ∘ ∘                                       Comparative 6  2 f  60 Δ ∘                                  example 7 5000-series 1 g  0.02 x x                                            8  -- -- -- -- x x                                                         __________________________________________________________________________

a: top: 10˜25 nm (sulfuric acid)/50˜120 nm (phosphoric acid): bottom

b: top: 20˜25 nm (sulfuric acid-oxalic acid)/30˜50 nm (sulfuricacid-oxalic acid)/30˜120 nm (phosphoric acid): bottom

c: top: 15˜50 nm (phosphoric acid)/60˜250 nm (phosphoric acid): bottom

d: top: 20˜25 nm (sulfuric acid-oxalic acid/30˜120 nm (phosphoricacid)/100˜120 nm (phosphoric acid)/100˜250 nm (phosphoric acid): bottom

e: top: 10˜15 nm (sulfuric acid)/30˜40 nm (sulfuric acid-oxalicacid)/100˜120 nm (phosphoric acid)/80˜100 nm (phosphoric acid)/80˜250 nm(phosphoric acid): bottom

f: top: 10 nm (sulfuric acid)/20 nm (sulfuric acid-oxalic acid): bottom

g: top: 20 nm (sulfuric acid): bottom

The anodic oxide coating of the test pieces Nos. 1 to 5 had a porouslayer including two or more layers and having pores with a diameterwhich changed continuously. As is obvious from the results shown inTable 5, the test pieces Nos. 1 to 5, satisfying the conditions of thepresent invention, exhibited the excellent resistance to gas corrosionand plasma. On the other hand, the test pieces Nos. 6 to 8,corresponding to the comparative examples and not satisfying one or moreconditions of the present invention, exhibited the insufficientresistance to gas corrosion and/or plasma.

EXAMPLE 6

As shown in Table 6, various aluminum alloy plates were provided with ananodic oxide coating having different structure from each other. InExample 6, an oxalic acid solution was used as an electrolytic solution.These aluminum alloy plates were used as test pieces. Table 6 also showsthe change in structure of each porous layer by means of a pore diameterand the thickness of each anodic oxide coating.

Repeating the gas corrosion test and the plasma irradiation testconducted in Example 4, the test pieces were tested to evaluate theirresistance to gas corrosion and plasma. The test results are shown inTable 6.

                                      TABLE 6                                     __________________________________________________________________________                  Structure of                                                      porous layer  Thickness of Gas Plasma                                               Kind of                                                                             Numbers of                                                                          Pore Treatment                                                                          anodic oxide                                                                        corrosion                                                                          irradiation                            No. Al alloy layer diameter method coating (μm) test test                __________________________________________________________________________    Example of                                                                          1 5000-series                                                                         2     a    oxalic                                                                             30    ∘                                                                      ∘                          present 2  2 b acid 0.2 ∘ ∘                           invention 3  3 c anodizing 5 ∘ ∘                       4 6000-series 2 d  35 ∘ ∘                             5  5 e  0.8 ∘ ∘                                      Comparative 6  2 f  60 Δ ∘                                  example 7 1000-series 1 g  0.03 x x                                            8 5000-series 1 h  2 x Δ                                                9  -- -- -- -- x x                                                         __________________________________________________________________________

a: top: 10˜20 nm/30˜200 nm: bottom

b: top: 20˜25 nm/80˜160 nm: bottom

c: top: 15˜15 nm/50˜100 nm/80˜160 nm: bottom

d: top: 20˜25 nm/100˜250 nm: bottom

e: top: 10˜15 nm/30˜50 nm/80˜120 nm/80˜120 nm/80˜250 nm: bottom

f: top: 10 nm/20 nm: bottom

g: top: 20 nm: bottom

h: top: 10 nm: bottom

The test pieces Nos. 1 to 5 had a porous layer including two or morelayers having pores with a diameter which changed continuously. As isobvious from the results shown in Table 6, the test pieces Nos. 1 to 5,satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand,test pieces Nos. 6 to 9, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 7

As shown in Table 7, various aluminum alloy plates were provided with ananodic oxide coating having different structure from each other. Thesealuminum alloy plates were used as test pieces. Table 7 also shows thenumber of layers included in each porous layer, a pore diameter at a topand a bottom of each porous layer, kinds of electrolytic solutions usedfor anodizing, and the thickness of each anodic oxide coating.

In order to evaluate the corrosion resistance to a halogen-containinggas for the test pieces, a gas corrosion test was conducted by using 10%of mixed gas of Cl₂ and Ar at a temperature of 350° C. for 4 hours. Uponthe completion of the test, the appearance of test pieces was evaluatedunder the following standards.

<Gas Corrosion Test>

⊚: No corrosion was generated.

∘: Corrosion was generated in an area of less than 5% of test piece.

Δ: Corrosion was generated in an area in the range between 5% or moreand less than 10% of test piece.

x: Corrosion was generated in an area of 10% or more of test piece.

In addition, in order to evaluate the resistance to plasma for the testpieces, a chlorine plasma irradiation test was conducted under the lowbias for 120 minutes. Upon completion of the test, the etched depth ofthe test pieces was measured and evaluated under the followingstandards.

<Plasma Irradiation Test>

⊚: Test piece was etched in a depth of less than 1.5 μm.

∘: Test piece was etched in a depth in the range between 1.5 μm or moreand less than 2 μm.

Δ: Test piece was etched in a depth in the range between 2 μm or moreand less than 5 μm.

x: Test piece was etched in a depth of 5 μm or more.

The results of gas corrosion test and the plasma irradiation test areshown in Table 7.

                                      TABLE 7                                     __________________________________________________________________________                              Originally contained                                                                    Components    Thickness                      compound + added contained in  of anodic Gas Plasma                          Structure of porous layer compound coating  oxide cor- irradia-                     Kind of                                                                           Number                                                                             Pore diameter (nm)                                                                     Mark "/" indicates that each layer                                                               Treatment                                                                          coating                                                                            rosion                                                                            tion                 Al alloy of layers top/bottom contains different compound method                                                                       (μm) test                                                                  test               __________________________________________________________________________    Example of                                                                          1 1000-                                                                             2    20/100   H.sub.3 PO.sub.4 /(COOH).sub.2                                                          4% P/0.015% C                                                                          anodizing                                                                          4    ◯                                                                     ◯        present 2 series 2 20/100 H.sub.3 PO.sub.4 + HF/ 4% P + 0.02% F/  3                                                                    .circleincircle                                                               . ◯      invention     (COOH).sub.2 + HF 2% C + 0.02% F                                 3  3 50/30/70 (COOH).sub.2 + Al.sub.2 (SO.sub.4).sub.2 2% C + 0.03% S                                                                 0.1 .circleinci                                                               rcle. .largecir                                                               cle.                  4 6000- 2 10/120 H.sub.2 SO.sub.4 + H.sub.3 PO.sub.3 / 4% S + 0.02 P                                                                  %/  3 .circlein                                                               circle.                                                                       ◯                                                                    series                                                                     (COOH).sub.2 +                                                                H.sub.3                                                                       PO.sub.3 1.8%                                                                 C + 0.02% P                                                                     5  3                                                                        15/40/150                                                                     H.sub.3                                                                       PO.sub.4 +                                                                    Al(NO.sub.3).su                                                               b.3 3% P +                                                                    0.025% N  30                                                                  .circleincircle                                                               . .circleincirc                                                               le.                   6  5 30/50/80/200 H.sub.3 PO.sub.4 + (COOH).sub.2 4% P + 0.03% C  1.5                                                                 .circleincircle                                                               . ◯       7 5000- 6 20/120/20/ (COOH).sub.2 + H.sub.2 SO.sub.4 2% C + 0.2% S  35                                                                ◯                                                                 .circleincircle                                                               .                      series  120/20/180                                                           8  6 20/120/20 (COOH).sub.2 + HNO.sub.3 2% C + 0.04% N  5 .circleincirc                                                               le. .circleinci                                                               rcle.                    120/20/180                                                                 9  2 5/10 H.sub.2 SO.sub.4 + H.sub.3 BO.sub.3 3% S + 0.025% B  0.2                                                                    .circleincircle                                                               . ◯      Comparative 10  1 5 (COOH).sub.2 2% C  30 Δ Δ                     example 11 6000- -- -- -- -- -- -- X X                                          series                                                                       12 1000- 2 10/50 H.sub.3 PO.sub.4 3% P anodizing 0.03 X X                     13 series 2 80/15 H.sub.3 PO.sub.4 + H.sub.2 SO.sub.4 3% P + 0.1% S                                                                   70 Δ                                                                    Δ            __________________________________________________________________________

As is obvious from the results shown in Table 7, the test pieces Nos. 1to 9, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 10 to 13, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 8

As shown in Table 8, various aluminum alloy plates were provided with ananodic oxide coating having different structure from each other. Thesealuminum alloy plates were used as test pieces. Table 8 also shows thechange in the structure of each porous layer by means of a porediameter, kinds of electrolytic solutions used in anodizing, and thethickness of each anodic oxide coating.

The test pieces were tested to evaluate their resistance to gascorrosion and plasma repeating the gas corrosion test and the plasmairradiation test conducted in Example 7, except that the gas corrosiontest was conducted at 350° C. for 5 hours and the chlorine plasmairradiation test was conducted for 150 minutes. The test results areshown in Table 8.

                                      TABLE 8                                     __________________________________________________________________________                        Originally contained      Thickness of                                                                        Gas   Plasma                 Kind of Structure* compound + Components contained Treatment anodic                                                                  oxide corrosion                                                               irradiation                                                                    No. Al alloy                                                                 of coating                                                                    added compound                                                                in coating                                                                    method coating                                                                (μm) test                                                                  test                __________________________________________________________________________    Example                                                                             1  1000-series                                                                         a    (COOH).sub.2 + H.sub.3 PO.sub.4                                                         1.5% C + 0.03% P                                                                        anodizing                                                                           2.8   ⊚                                                                    ◯                                                                  of 2 6000-serie                                                              s b H.sub.3                                                                   PO.sub.4 + HF                                                                 3% P + 0.02% F                                                                10 ◯                                                               ◯                                                                 present 3  b                                                                 H.sub.3                                                                       PO.sub.4 +                                                                    H.sub.2                                                                       SO.sub.4 3% P +                                                               0.04% S  8                                                                    ⊚                                                               .circleincircle                                                              .                     invention 4  c H.sub.2 SO.sub.4 + HNO.sub.3 4% S + 0.5% N  38 .circleinc                                                              ircle. .circlein                                                              circle.                                                                         5 5000-series                                                               d (COOH).sub.2                                                                + H.sub.3                                                                     BO.sub.3 1.5% C                                                               + 0.03% B  0.07                                                               ◯                                                                 ◯                                                                   6  d (COOH).su                                                              b.2 + HF 1.5% C                                                               + 0.02% F  0.06                                                               ⊚                                                               ◯                                                                  7  e H.sub.3                                                                PO.sub.4 +                                                                    H.sub.2                                                                       CO.sub.3 3% P +                                                               0.04% C  20                                                                   ⊚                                                               .circleincircle                                                              .                     Comparative 8  f H.sub.3 PO.sub.4 3% P  0.03 X X                              example 9 6000-series g (COOH).sub.2 1.5% C  43 Δ Δ                                                                         10  h H.sub.3                                                               PO.sub.4 +                                                                    Al(NO.sub.3).sub                                                              .3 3% P + 0.1%                                                                N  80 X X                                                                       11  -- -- --                                                                -- X X              __________________________________________________________________________     *Remarks: Structure of coating: indicated by means of pore diameter           a: top: 20˜300 nm: bottom                                               b: top: 15˜200 nm: bottom                                               c: top: 3˜5˜10˜15 nm: bottom                                d: top: 6˜180 nm: bottom                                                e: top: 29˜100 nm: bottom                                               f: top: 18˜18 nm: bottom                                                g: top: 8˜8 nm: bottom                                                  h: top: 9˜15 nm: bottom                                            

As is obvious from the results shown in Table 8, the test pieces Nos. 1to 7, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 8 to 11, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 9

As shown in Table 9, various aluminum alloy plates were provided with ananodic oxide coating having different structure from each other. Thesealuminum alloy plates were used as test pieces. Table 9 also shows thechange in the structure of each porous layer by means of a porediameter, kinds of electrolytic solutions used in anodizing, and thethickness of each anodic oxide coating.

The test pieces were tested to evaluate their resistance to gascorrosion and plasma repeating the gas corrosion test and the plasmairradiation test conducted in Example 7, except that the gas corrosiontest was conducted at a temperature of 370° C. for 5 hours and thechlorine plasma irradiation test was conducted for 180 minutes. The testresults are shown in Table 9.

                                      TABLE 9                                     __________________________________________________________________________                 Number of  Originally contained                                                                   Components    Thickness of                                                                        Gas  Plasma                 Kind of layers in Structure* compound + contained in Treatment anodic                                                                oxide corrosion                                                               irradiation                                                                    No. Al alloy                                                                 porous layer of                                                               coating added                                                                 compound                                                                      coating method                                                                coating (μm)                                                               test test           __________________________________________________________________________    Example of                                                                          1 5000-                                                                              2     a    (COOH).sub.2 + HF                                                                      1.5% C + 0.03% F                                                                       anodizing                                                                          17    ⊚                                                                   ⊚      present 2 series 3 b H.sub.3 PO.sub.4 + HF 3% P + 0.02% F  0.1 .largecir                                                              cle. .largecircl                                                              e.                    invention 3  3 b H.sub.3 PO.sub.4 + HNO.sub.3 3% P + 0.02% N  0.09                                                                    ⊚                                                               ◯                                                                  4 6000- 2 c                                                                 H.sub.2                                                                       SO.sub.4 +                                                                    (COOH).sub.2 /                                                                5% S + 0.02% C/                                                                30 .circleincir                                                              cle. .circleinci                                                              rcle.                   series   H.sub.3 PO.sub.4 + (COOH).sub.2 2% P + 0.02% C                      5  4 d (COOH).sub.2 + H.sub.2 SO.sub.4 1.5% C + 0.04% S  3 .circleincir                                                              cle. .largecircl                                                              e.                     6  5 e (COOH).sub.2 + H.sub.3 BO.sub.3 1.5% C + 0.05% B  40 .circleinci                                                              rcle. .circleinc                                                              ircle.                Comparative 7  2 f (COOH).sub.2 3% P  60 Δ Δ                      example 8 5000- 1 g (COOH).sub.2 1.5% C  0.02 X X                              9 series -- -- -- -- -- -- X X                                             __________________________________________________________________________     *Structure: pore diameter of each layer                                       a: top: 8˜20 nm/45˜160 nm: bottom                                 b: top: 17˜27 nm/35˜48 nm/27˜150 nm: bottom                 c: top: 8˜25 nm/57˜280 nm: bottom                                 d: top: 18˜27 nm/34˜130 nm/110˜125 nm/110˜280 nm:     bottom                                                                        e: top: 12˜17 nm/35˜45 nm/90˜100 nm/85˜110            nm/85˜270 nm: bottom                                                    f: top: 10 nm/25 nm: bottom                                                   g: top: 15 nm: bottom                                                    

As is obvious from the results shown in Table 9, the test pieces Nos. 1to 6, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand,test pieces Nos. 7 to 9, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 10

As shown in Table 10, various aluminum alloy plates were used as testpieces, which had a composition satisfying the requirements of JapaneseIndustrial Standard. The aluminum alloy plates were dissolved in theatmosphere and casted at a rate of 1° C./sec. The resultant was thenannealed for homogenization at 480° C. for 4 hours, and after that, wassubjected to hot extrusion or hot rolling at 450° C. The reduction rateof thickness by hot rolling was 80% and the extrusion ratio of the hotextrusion was 4.

Using a scanning electron microscope, a cross section of the test pieceswas observed to obtain an average diameter of precipitates and/ordeposits. Some of test pieces were subjected to image analysis tocalculate their volumetric proportion. An average diameter, a volumetricproportion, and an arrangement direction of precipitates and/or depositsare shown in Table 10. In Example 10, an arrangement direction indicatesthe direction along which precipitates and/or deposits are arranged withrespect to the largest area of test piece to which the following gascorrosion resistance test and the plasma resistance test were conducted.

<Gas Corrosion Test>

In order to evaluate the corrosion resistance to a halogen-containinggas for the test pieces, a gas corrosion test was conducted by using 5%of mixed gas of Cl₂ and Ar at a temperature of 400° C. for 2 hours. Uponcompletion of the test, the appearance of test pieces was evaluatedunder the following standards.

<Gas Corrosion Test>

⊚: No corrosion was generated.

∘: Corrosion was generated in an area of less than 10% of test piece.

Δ: Corrosion was generated in an area in the range between 10% or moreand less than 20% of test piece.

x: Corrosion was generated in an area of 20% or more of test piece.

In addition, in order to evaluate the resistance to plasma for the testpieces, a chlorine plasma irradiation test was conducted under the lowbias. 15 minutes of plasma irradiation was repeated 6 times at 5 minuteintervals. Upon completion of the test, the test pieces were evaluatedunder the standards same as those used for the gas resistance test.

The results of gas corrosion test and the plasma irradiation test areshown in Table 10.

                                      TABLE 10                                    __________________________________________________________________________                              Average grain diameter (μm)/                       Pore diameter Coating volumetric proportion (%)  Gas Plasma                         Kind of                                                                             (anodizing                                                                           thickness                                                                          Crystallized                                                                         Deposited                                                                           Arrangement                                                                         corrosion                                                                           irradiation                  No. Al alloy solution) μm particles particles direction test             __________________________________________________________________________                                                       test                       Example of                                                                          1 2000-series                                                                         20(S)/80(P)                                                                          0.5  1/1.0  2/1.5 parallel                                                                             ⊚                                                                   ⊚                                                               present 2  20(S)/80(P)                                                        0.5 3/-- 2/--                                                                perpendicular .largecir                                                       cle. ◯                                                             invention 3 5000-serie                                                       s 10(S)/80(P) 10 4/1.5                                                        3/2.5 parallel                                                                ◯ .circlein                                                       circle.                       4  10(S)/80(P) 10 10/-- 10/-- perpendicular ◯ .circleincirc                                                       le.                           5 1000-series 15/40/80(O) 2 1/0.8 2/1.2 parallel ⊚                                                             ⊚                                                                6  15/40/80(O) 2                                                            2/0.5 1/0.8 perpendicul                                                       ar ◯                                                              ⊚                                                                7 6000-series                                                               15/40/80(O) 15 3/--                                                           2/-- parallel .circlein                                                       circle. .circleincircle                                                       .                             8  15/40/80(O) 15 8/-- 10/-- parallel ◯ ◯                                                               9  15/40/80(O) 15                                                           8/1.5 12/1.8 perpendicu                                                       lar ◯                                                             ◯                 10 1000-series 10˜110(O) 25 3/0.8 1/0.8 parallel ⊚                                                        ⊚                                                               11  10˜110(O)                                                         25 11/2.5 8/1.8                                                               perpendicular .largecir                                                       cle. ◯                                                              12 6000-series                                                              10˜90(S .multidot                                                       . O) 2 2/-- 1/--                                                              parallel .circleincircl                                                       e. ⊚                                                             13  10˜90(S                                                           · O) 2 2/1.8                                                         3/0.8 perpendicular                                                           ◯ .largecir                                                       cle.                          14 7000-series 20˜150(O) 30 2/-- 4/-- parallel ◯                                                            ⊚                                                                15  20˜150(O)                                                         30 10/1.8 10/1.8                                                              perpendicular .largecir                                                       cle. ◯                                                              16  20˜150(O)                                                         30 10/1.8 10/2.0                                                              parallel ◯                                                        ⊚                                                               Comparative 17                                                               1000-series 15(S) 7                                                           3/0.8 3/0.8 parallel                                                          Δ Δ                                                                example 18  15(S) 7                                                          8/-- 5/-- perpendicular                                                        X Δ                    19 3000-series 30(S · O) 10 3/-- 2/-- parallel Δ                                                               ◯                 20  30(S · O) 10 3/-- 2/-- perpendicular Δ Δ                                                               21 5000-series 80(P)                                                        5 4/1.2 3/0.8 parallel                                                        ◯ Δ                                                           22  80(P) 5 10/2.5                                                          10/1.8 perpendicular                                                          Δ X                     23  80(P) 8 8/-- 12/-- perpendicular X X                                      24 6000-series 10(S) 8 2/0.8 3/1.2 parallel Δ ◯                                                               25  10(S) 8 4/1.6                                                           6/2.1 parallel Δ                                                        ◯                 26  15(S) 15 12/-- 8/-- perpendicular X Δ                               27  20(S) 15 12/-- 11/-- perpendicular X X                                 __________________________________________________________________________

As is obvious from the results shown in Table 10, the test pieces Nos. 1to 16, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 17 to 27, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 11

As shown in Table 11, various aluminum alloy plates were provided withan anodic oxide coating having different structure from each other byapplying electrolytic voltage of various patterns shown in FIGS. 1 and2. These aluminum alloy plates were used as test pieces.

The patterns A to F shown in FIG. 4 illustrate the preferableelectrolytic voltage application in the surface treatment method of thepresent invention. At least the final voltage is higher than the initialvoltage, and the change in electrolytic voltage is continuous.Therefore, the anodic oxide coating produced by applying theelectrolytic voltage of patterns A to F corresponds to the examples ofthe present invention. On the other hand, the pattern G in FIG. 5illustrates an electrolytic voltage application which is controlled insuch a manner that the initial voltage is higher than the final voltage.Therefore, the anodic oxide coating produced by applying theelectrolytic voltage of pattern G corresponds to the comparativeExample. The pattern H in FIG. 5 illustrates an electrolytic voltageapplication which is controlled to be constant in the entire anodizingprocess. Therefore, the anodic oxide coating produced by applying anelectrolytic voltage of pattern H corresponds to a conventional example.

Table 11 also shows a composition of anodizing solution, the initialvoltage, and the final voltage (also shown are voltages at points wherethe voltage application are changed in the process of anodizing.).

In order to evaluate the corrosion resistance to a halogen-containinggas for the test pieces, a gas corrosion test was conducted by using 5%of mixed gas of Cl and Ar at a temperature of 300° C. for 4 hours. Uponcompletion of the test, the appearance of test pieces was evaluatedunder the following standards.

<Gas Corrosion Test>

∘: No corrosion was generated.

Δ: Corrosion was generated in an area of less than 5% of test piece.

x: Corrosion was generated in an area of 5% or more of test piece.

In addition, in order to evaluate the resistance to plasma of the testpieces, a chlorine plasma irradiation test was conducted under the lowbias for 90 minutes. Upon completion of the test, the etched depth ofthe test pieces was measured and evaluated under the followingstandards.

<Plasma Irradiation Test>

∘: Test piece was etched in a depth of less than 2 μm.

Δ: Test piece was etched in a depth in the range between 2 μm or moreand less than 5 μm.

x: Test piece was etched in a depth of 5 μm or more.

The results of gas corrosion test and the plasma irradiation test areshown in Table 11.

                                      TABLE 11                                    __________________________________________________________________________                      Composition of                                                                          Initial voltage˜                                                                Gas  Plasma                                  Kind of Voltage anodizing solution Final voltage corrosion irradiation       No. Al alloy pattern kind and concentration (V) test test                   __________________________________________________________________________    Example of                                                                          1 1000-series                                                                         A   sulfuric acid 100 g/l                                                                   5˜30                                                                            ◯                                                                      ◯                          present 2 2000-series B phosphoric acid 40 g/l 50˜100 .largecircle                                             . ◯                        invention 3 5000-series C oxalic acid 60 g/ 20˜60˜80                                                     ◯ ◯                                                     4  D phosphoric acid 30 g/l                                                 40˜20˜120 .largecircl                                             e. ◯                        5 6000-series A oxalic acid 10 g/l 20˜60 ◯ .largecirc                                             le.                                     6  E oxalic acid 30 g/l 5˜50˜20˜60˜80 .largecir                                             cle. ◯                      7 3000-series F oxalic acid 30 g/l 40˜60˜20˜100                                                   ◯ ◯                                                     8 6000-series B sulfuric acid                                               150 g/l 10˜20 Δ                                                   ◯                          Comparative 9 5000-series G oxalic acid 30 g/l 80˜50 X Δ                                                  example 10  G sulfuric acid 100                                              g/l 20˜10 X Δ                                                       11 6000-series H phosphoric                                                 acid 30 g/l 60 Δ X                                                        12 1000-series H sulfuric acid                                              150 g/l 20 X Δ                    13 7000-series -- -- -- X X                                                __________________________________________________________________________

As is obvious from the results shown in Table 11, the test pieces Nos. 1to 8, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 9 to 13, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 12

As shown in Table 12, various aluminum alloy plates were provided withan anodic oxide coating having different structure from each other byapplying electrolytic voltage of various patterns shown in FIGS. 6 and7. These aluminum alloy plates were used as test pieces.

The patterns A to F shown in FIG. 6 illustrate the preferableelectrolytic voltage application in the surface treatment method of thepresent invention. At least the final voltage is higher than the initialvoltage, and the change in electrolytic voltage is continuous.Therefore, the anodic oxide coating produced by applying theelectrolytic voltage of patterns A to F correspond to the examples ofthe present invention. On the other hand, the pattern G in FIG. 7illustrates an electrolytic voltage application which is controlled tobe constant in the entire anodizing process, and the pattern H in FIG. 7illustrates an electrolytic voltage application which is controlled insuch a manner that the initial voltage and the final voltage areidentical to each other. Therefore, an anodic oxide coating produced byapplying an electrolytic voltage of patterns G and H corresponds to aconventional example.

Table 12 also shows a composition of anodizing solution, the initialvoltage, and the final voltage (also shown is a voltage value keptconstant for an arbitrary period during anodizing.).

Repeating the gas corrosion test and the plasma irradiation testconducted in Example 11, the test pieces were tested to evaluate theirresistance to gas corrosion and plasma. The test results are shown inTable 12.

                                      TABLE 12                                    __________________________________________________________________________                      Composition of anodizing                                                                  Initial voltage/                                                                     Gas  Plasma                                 Kind of Al Voltage solution Final voltage corrosion irradiation                                                       No. alloy pattern kind and                                                   concentration (V) test test         __________________________________________________________________________    Example of                                                                          1 1000-series                                                                         A   sulfuric acid 150 g/l                                                                     10/30  ◯                                                                      ◯                         present 2 2000-series B phosphoric acid 30 g/l 50/120 ◯                                                   ◯                         invention 3 5000-series C oxalic acid 60 g/l 30/60/80 ◯                                                   ◯                          4  A sulfuric acid 50 g/l/ 20/100 ◯ ◯                    phosphoric acid 50 g/l                                                     5 6000-series D oxalic acid 10 g/l 20/50/100 ◯ .largecircle                                              .                                      6  E oxalic acid 60 g/l 20/60/40/80 ◯ ◯                                                        7 3000-series F oxalic acid                                                 30 g/l 40/20/100 ◯                                                ◯                          8 6000-series B oxalic acid 30 g/l 60/100 ◯ Δ                                                       Comparative 9 5000-series A                                                  sulfuric acid 100 g/l 20/10 X                                                 Δ                               example 10  B oxalic acid 60 g/l 100/60 X Δ                              11 6000-series G phosphoric acid 30 g/l 50 Δ X                          12 1000-series H sulfuric acid 150 g/l 20 X Δ                           13 7000-series -- -- -- X X                                                __________________________________________________________________________

As is obvious from the results shown in Table 12, the test pieces Nos. 1to 8, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 9 to 13, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 13

As shown in Table 13, various aluminum alloy plates were provided withan anodic oxide coating having different structure from each other byapplying electrolytic voltage of various patterns shown in FIGS. 4 and5. These aluminum alloy plates were used as test pieces.

In order to evaluate the corrosion resistance to a halogen-containinggas of the test pieces, a gas corrosion test was conducted by using 5%of mixed gas of Cl and Ar at a temperature of 350° C. for 4 hours. Uponcompletion of the test, the appearance of test pieces was evaluatedunder the following standards.

<Gas Corrosion Test>

⊚: No corrosion was generated.

∘: Corrosion was generated in an area of less than 5% of test piece.

Δ: Corrosion was generated in an area in the range between 5% or moreand less than 10% of test piece.

x: Corrosion was generated in an area of 10% or more of test piece.

In addition, in order to evaluate the resistance to plasma of the testpieces, a chlorine plasma irradiation test was conducted under the lowbias for 100 minutes. Upon completion of the test, the etched depth ofthe test pieces was measured and evaluated their resistance to plasmarepeating the process of Example 11.

Test results of the gas corrosion test and the plasma irradiation testare shown in Table 13.

                                      TABLE 13                                    __________________________________________________________________________                      Composition of anodizing                                                                  Initial voltage ˜                                                               Gas  Plasma                                Kind of Voltage solution final voltage corrosion irradiation                 No. Al alloy pattern kind and concentration (V) test test                   __________________________________________________________________________    Example of                                                                          1 1000-series                                                                         A   oxalic acid 60 g/l                                                                        5˜30                                                                            ◯                                                                      ◯                        present    sulfuric acid 80 g/l                                               invention 2 2000-series B oxalic acid 15 g/l 50˜120 .circleincircl                                               e. ◯                         phosphorous acid 4 g/l                                                     3 5000-series C oxalic acid 3 g/l 20˜60˜80 ⊚                                                ◯                           phosphoric acid 40 g/l                                                     4  D oxalic acid 30 g/l 40˜20˜100 ⊚                                                        ◯                            ammonium borate 3 g/l                                                      5 6000-series A oxalic acid 15 g/l 5˜75 ⊚                                                        ◯                            sulfuric acid 3 g/l                                                        6  E oxalic acid 30 g/l 5˜50˜20˜60˜80 .largecir                                               cle. ◯                    7 3000-series F oxalic acid 30 g/l 40˜60˜20˜100                                                     ◯ ◯                                                        hydrofluoric acid 0.2 g/l        8 6000-series B oxalic acid 45 g/l 10˜20 Δ ◯                                                       sulfuric acid 50 g/l                                                      Comparative 9 5000-series G                                                  oxalic acid 30 g/l 80˜20                                                X Δ                            example 10  G oxalic acid 30 g/l 20˜10 X X                                  hydrofluoric acid 3 g/l                                                    11 6000-series H phosphoric acid 30 g/l 60 Δ X                          12 1000-series H sulfuric acid 150 g/l 15 X Δ                              phosphoric acid 5 g/l                                                      13 7000-series -- -- -- X X                                                __________________________________________________________________________

As is obvious from the results shown in Table 13, the test pieces Nos. 1to 8, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 9 to 13, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 14

As shown in Table 14, various aluminum alloy plates were provided withan anodic oxide coating having different structure from each other byapplying electrolytic voltage of various patterns shown in FIGS. 6 and7. These aluminum alloy plates were used as test pieces.

Repeating the gas corrosion test and the plasma irradiation testconducted in Example 13, the test pieces were tested to evaluate theirresistance to gas corrosion and plasma. The test results are shown inTable 14.

                                      TABLE 14                                    __________________________________________________________________________                      Composition of anodizing                                                                  Initial voltage/                                                                      Gas  Plasma                                Kind of Voltage solution Final voltage corrosion irradiation                 No. Al alloy pattern kind and concentration (V) test test                   __________________________________________________________________________    Example of                                                                          1 1000-series                                                                         A   oxalic acid 15 g/l                                                                        10/85   ⊚                                                                   ◯                        present    sulfuric acid 15 g/l                                               invention 2 2000-series B oxalic acid 30 g/l 25/120 ⊚                                                   ◯                            phosphoric acid 30 g/l                                                     3 5000-series C oxalic acid 50 g/l 30/60/80 ◯ ◯       4  A oxalic acid 10 g/l 10/120 ⊚ ◯                    sodium nitrate 50 g/l/                                                        oxalic acid 1 g/l                                                             phosphorous acid 50 g/l                                                    5 6000-series D oxalic acid 10 g/l 20/60/90 ⊚ .largecirc                                               le.                                      phosphoric acid 5 g/l                                                      6  E oxalic acid 60 g/l 10/30/40/80 ⊚ ◯                                                         sulfuric acid 10 g/l                                                       7 3000-series F oxalic acid                                                 30 g/l 45/30/100 ◯                                                ◯                            ammonium borate 5 g/l                                                      8 6000-series B oxalic acid 30 g/l 60/100 ◯ Δ                                                            hydrofluoric acid 0.5 g/l       Comparative 9 5000-series A sulfuric acid 100 g/l 20/10 X Δ                                                       example 10  B oxalic acid 60                                                 g/l 80/40 X X                            hydrofluoric acid 2 g/l                                                    11 6000-series G phosphoric acid 30 g/l 50 Δ X                             sulfuric acid 2 g/l                                                        12 1000-series H sulfuric acid 120 g/l 20 X Δ                           13 7000-series -- -- -- X X                                                __________________________________________________________________________

As is obvious from the results shown in Table 14, the test pieces Nos. 1to 8, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 9 to 13, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 15

As shown in Table 15, various aluminum alloy plates were subjected to aporous-type anodizing and/or a non-porous type anodizing to be providedwith an anodic oxide coating having different structure from each other.These aluminum alloy plates were used as test pieces. Table 15 alsoshows the structures of each porous layer and each barrier layer andkinds of electrolytic solutions used for anodizing.

In order to evaluate the corrosion resistance to a halogen-containinggas for the test pieces, a gas corrosion test was conducted by using 5%of mixed gas of Cl₂ and Ar at a temperature of 350° C. for 4 hours. Uponcompletion of the test, the appearance of test pieces was evaluatedunder the following standards.

<Gas Corrosion Test>

∘: No corrosion was generated.

Δ: Corrosion was generated in an area of less than 5% of test piece.

x: Corrosion was generated in an area of 5% or more of test piece.

In addition, in order to evaluate the resistance to plasma of the testpieces, a chlorine plasma irradiation test was conducted under the lowbias for 90 minutes. Upon completion of the test, the etched depth ofthe test pieces was measured and evaluated under the followingstandards.

<Plasma Irradiation Test>

∘: Test piece was etched in a depth of less than 2 μm.

Δ: Test piece was etched in a depth in the range between 2 μm or moreand less than 5 μm.

x: Test piece was etched in a depth of 5 μm or more.

The results of the gas corrosion test and the plasma irradiation testare shown in Table 15.

                                      TABLE 15                                    __________________________________________________________________________                  Structure and kind of coating                                                                    Gas  Plasma                                          Kind of         Barrier                                                                           Treatment                                                                          corrosion                                                                          irradiation                               No. Al alloy Porous layer layer method test test                            __________________________________________________________________________    Example of                                                                          1 1000-series                                                                         20(15) - S                                                                              0.05 - B                                                                          anodizing                                                                          ◯                                                                      ◯                             present 2  5(15) - S/5(30) - O 0.1 - F  ◯ ◯                                                invention 3 6000-series 15(20) - S                                           0.05 - B  ◯ .largecircle                                          .                                          4  tapered layer - O 0.15 - F  ◯ ◯                    5  10(15) - S/5(40) - SO 0.15 - B  ◯ ◯                                                     6  5(30) - O 0.1 - P  .largecircle                                          . ◯                            7 5000-series 15(10) - S/5(10) - O 0.1 - B  ◯ ◯         5(70) - O                                                                   8  25(20) - SO 0.2 - B  ◯ ◯                          Comparative 9  -- 0.05 - B  Δ X                                         Example 10 6000-series -- -- -- X X                                            11 1000-series 2(120) - P/10(20) - S -- anodizing X Δ                   12  50(10) - S --  X Δ                                               __________________________________________________________________________     In the column "Structure and kind of coating",                                (i) Alphabet capital letters represent:                                       P: phosphoric acid                                                            S: sulfuric acid                                                              O: oxalic acid                                                                SO: sulfuric acid + oxalic acid                                               B: boric acid + ammonium borate                                               F: potassium hydrogen phthalate                                               (ii) Numbers indicate the thickness of anodic oxide coating(unit μm),      where numbers in () indicate pore diameter (unit: nm).                        Marks "/" indicate that the structure of porous layer is different betwee     at the top and at the bottom.                                                 (iii) For example, "5(15)  S/5(30)  O" of test piece No. 2 indicates: top     of porous layer; thickness of 5 μm (pore diameter of 15 nm)  anodizing     solution: sulfuric acid bottom of porous layer; thickness of 5 μm (por     diameter of 30 nm)  anodizing solution: oxalic acid                      

As is obvious from the results shown in Table 1, the test pieces Nos. 1to 8, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 9 to 12, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 16

As shown in Table 16, various aluminum alloy plates were subjected to aporous-type anodizing by applying an electrolytic voltage of variouspatterns shown in FIGS. 6 and 7, and then were subjected to a non-poroustype anodizing. These aluminum alloy plates were used as test pieces.Table 16 also shows kinds of electrolytic solutions and an anodizingvoltage used for the porous-type anodizing and the non-porous anodizing.

The resistance to gas corrosion and plasma of test pieces were evaluatedrepeating the process conducted in Example 15. The test results areshown in Table 16.

                                      TABLE 16                                    __________________________________________________________________________                      anodizing solution                                                                     porous type voltage/                                                                     Gas  Plasma                                Kind of Voltage porous type/ non-porous type voltage corrosion                                                        irradiation                          No. Al alloy pattern non-porous type (V) test test                          __________________________________________________________________________    Example of                                                                          1 1000-series                                                                         G   S/B      10/200     ◯                                                                      ◯                        present 2 2000-series C O/F 15,20,70/120 ◯ ◯                                                    invention 3 5000-series A S,                                                 SO/B 10,40/150 ◯                                                  ◯                         4  B SO/F 20,80/100 ◯ ◯                               5 6000-series H P/B ˜60/200 ◯ ◯                 6  A S, O/B 20,40/250 ◯ ◯                             7 3000-series G SO/B 20/150 ◯ ◯                       8 6000-series D SO, O/F 10(S0, 30(0) ◯ Δ                        90(0)/350                                                                Comparative 9 5000-series G S 10 X Δ                                    example 10  H SO ˜40 X Δ                                           11 6000-series C P/S 10,20,40/20 Δ X                                    12 1000-series A S 15,30 X Δ                                            13 7000-series -- -- -- X X                                                __________________________________________________________________________

As is obvious from the results shown in Table 16, the test pieces Nos. 1to 8, satisfying the conditions of the present invention, exhibited theexcellent resistance to gas corrosion and plasma. On the other hand, thetest pieces Nos. 9 to 13, corresponding to the comparative examples andnot satisfying one or more conditions of the present invention,exhibited the insufficient resistance to gas corrosion and/or plasma.

EXAMPLE 17

As shown in Table 17, various aluminum alloy plates were used as testpieces, which had a composition satisfying the requirements of JapaneseIndustrial Standard. The aluminum alloy plates were dissolved in theatmosphere and casted at a rate of 1° C./sec. The resultant was thenannealed for homogenization at 480° C. for 4 hours, and after that, wassubjected to hot extrusion or hot rolling at 450° C. The reduction rateof thickness by hot rolling was 80% and the extrusion ratio of the hotextrusion was 4.

Using a scanning electron microscope, a cross section of the test pieceswas observed to obtain an average diameter of precipitates and/ordeposits. The test pieces were subjected to image analysis to calculatetheir volumetric proportion. An average diameter, a volumetricproportion, and an arrangement direction of precipitates and/or depositsare shown in Tables 17 and 18. In Example 17, an arrangement directionindicates the direction along which precipitates and/or deposits arearranged with respect to the largest area of test piece to which the gascorrosion resistance test and the plasma resistance test were conducted.

<Gas Corrosion Test>

In order to evaluate the corrosion resistance to a halogen-containinggas for the test pieces, a gas corrosion test was conducted by using 5%of mixed gas of Cl₂ and Ar at a temperature of 130° C. for 1 hour. Uponcompletion of the test, the maximum depth of the chlorine penetration ofthe test pieces was measured and evaluated under the followingstandards.

⊚: Test piece was penetrated by chlorine in a depth of less than 30 μmat maximum.

∘: Test piece was penetrated by chlorine in a depth in the range between30 μm or more and less than 50 μm.

Δ: Test piece was penetrated by chlorine in a depth in the range between50 μm or more and less than 100 μm.

x: Test piece was penetrated by chlorine in a depth of 100 μm or more.

<Plasma Resistance Test>

In addition, in order to evaluate the resistance to plasma of the testpieces, a chlorine plasma irradiation test was conducted under the lowbias for 15 minutes. Upon completion of the test, the maximum depth ofthe chlorine penetration of the test pieces was measured and evaluatedunder the same standards as those used for the gas resistance test.

The results of the gas corrosion test and the plasma irradiation testare shown in Tables 17 and 18.

                                      TABLE 17                                    __________________________________________________________________________             Average diameter (μm)/                                              volumetric proportion (%)  Gas Plasma                                          Kind of                                                                             Crystallized                                                                        Deposited                                                                           Arrangement                                                                          corrosion                                                                          irradiation                                    No. Al alloy particles particles direction test test Remarks                __________________________________________________________________________    1  1000-series                                                                         2/0.6 2/1.0 parallel                                                                             ⊚                                                                   ⊚                                                                   Example                                   2  5/1.3 7/2.0 parallel ⊚ ◯ of                     3  2/1.0 1/0.8 perpendicular ⊚ ⊚ present                                             4 2000-series 4/1.0 2/1.0 parallel                                           ⊚ ⊚                                             invention                                 5 3000-series 6/2.5 5/2.0 parallel ◯ ◯                6 5000-series 2/1.0 2/1.0 parallel ⊚ ⊚                                               7  6/2.0 2/2.0 parallel .circleinci                                          rcle. ◯                       8  3/1.0 2/1.5 perpendicular ◯ ◯                      9  8/3.0 8/2.5 parallel ◯ ◯                           10  2/5.0 1/3.0 perpendicular ◯ ◯                     11 6000-series 4/3.0 3/1.0 parallel ◯ ◯                                                    12  6/2.0 5/0.8 parallel .largecirc                                          le. ◯                         13  1/1.0 1/0.2 parallel ⊚ ⊚                    14  2/0.5 0.8/0.8 perpendicular ⊚ ⊚                                                  15  5/1.2 1.5/1.5 parallel                                                   ⊚ ⊚                                              16 7000-series 3/1.0 3/1.5                                                   parallel ⊚ .largecirc                                          le.                                       17  5/1.2 2/0.8 parallel ⊚ ◯                     __________________________________________________________________________

                                      TABLE 18                                    __________________________________________________________________________             Average diameter (μm)/                                              volumetric proportion (%)  Gas Plasma                                          Kind of                                                                             Crystallized                                                                        Deposited                                                                           Arrangement                                                                          corrosion                                                                          irradiation                                    No. Al alloy particles particles direction test test Remarks                __________________________________________________________________________    18 1000-series                                                                         2/1.5 11/0.5                                                                              perpendicular                                                                        X    Δ                                                                            Comparative                               19 2000-series 6/3.0 3/4.0 perpendicular X Δ example                    20 5000-series 11/3.0 7/3.0 perpendicular X X                                 21  11/4.0 10/1.5 perpendicular X X                                           22 6000-series 11/2.0 11/2.0 perpendicular X X                                23  12/1.0 3/0.8 perpendicular Δ X                                      24  15/0.8 12/0.8 perpendicular X X                                           25 7000-series 12/2.0 4/3.5 perpendicular X X                               __________________________________________________________________________

As is obvious from the results shown in Tables 17 and 18, the testpieces Nos. 1 to 17, satisfying the conditions of the present invention,exhibited the excellent resistance to gas corrosion and plasma. On theother hand, the test pieces Nos. 18 to 25, corresponding to thecomparative examples and not satisfying one or more conditions of thepresent invention, exhibited the insufficient resistance to gascorrosion and/or plasma.

EXAMPLE 18

As shown in Table 19, various aluminum alloy plates were subjected tosurface treatment. These aluminum alloy plates were used as test pieces.In Example 18, a corrosion test was conducted under the conditions moresevere than those used in Example 17, and the resistance to gascorrosion and plasma of the test pieces was evaluated.

<Gas Corrosion Test>

In order to evaluate the corrosion resistance to a halogen-containinggas of the test pieces, a gas corrosion test was conducted by using 5%of mixed gas of Cl₂ and Ar at a temperature of 350° C. for 4 hours. Uponcompletion of the test, the corroded area of test pieces was measuredand evaluated under the following standards.

⊚: Corrosion was generated in an area of less than 5%.

∘: Corrosion was generated in an area in the range between 5% or moreand less than 10% of test piece.

Δ: Corrosion was generated in an area in the range between 10% or moreand less than 20% of test piece.

x: Corrosion was generated in an area of 20% or more of test piece.

<Plasma Irradiation Test>

In order to evaluate the resistance to plasma of the test pieces, achlorine plasma irradiation test was conducted under the low bias. 15minutes of plasma irradiation was repeated 6 times at 5 minuteintervals. Upon completion of the test, the corroded area of the testpieces was measured and evaluated under the same standards as those usedfor gas corrosion test.

The results of the gas corrosion test and the plasma irradiation testare shown in Table 19.

                                      TABLE 19                                    __________________________________________________________________________              Average diameter (μm)/                                                                        Surface treatment                                  volumetric proportion (%)  method Gas Plasma                                    Kind of                                                                             Crystallized                                                                        Deposited                                                                           Arrangement                                                                          a Kind of coating                                                                      corrosion                                                                          irradiation                          No. Al alloy particles particles direction b Coating thickness test         __________________________________________________________________________                                               test                               1 a 5000-series                                                                         6/1   3/1   parallel                                                                             sputtering                                                                             ⊚                                                                   ⊚                      b  2/0.3 1/0.8 perpendicular a Al2O3 ⊚ ⊚        c  10/3 4/2 parallel b 2 μm ◯ ◯                    d  11/-- 10/-- perpendicular  X X                                            2 a 6000-series 4/1.2 2/1.5 parallel detonation flame ⊚                                                 ⊚                      b  6/1.5 3/2.5 perpendicular spraying ◯ ◯                                                       c  11/4.0 1/0.8 parallel a                                                  Al2O3 ◯ .largecircl                                               e.                                    d  12/5.0 3/2.5 perpendicular b 25 μm X X                                 2 a 1000-series 2/1 1/1 parallel sputtering ⊚ .circleinci                                               rcle.                                 b  4/2.5 2/2.0 perpendicular a TiO2 ◯ ◯                                                         c  2/4.2 8/2.5 parallel b 2                                                 μm ◯ .circleinci                                               rcle.                                 d  11/0.3 1/0.3 perpendicular  X X                                           4 a 6000-series 4/1 2/4 parallel anodizing ⊚ .circleincir                                               cle.                                  b  4/3.0 2/3.0 perpendicular a oxide layer ◯ ◯        c  8/0.5 4/1.2 parallel b 20 μm Δ ◯                      d  12/5 3/0.3 perpendicular  X X                                             5 a 1000-series 2/1 1/0.8 parallel sputtering ⊚ .circlein                                               circle.                               b  4/1 2/0.2 perpendicular a AlN ◯ ⊚                                                         c  4/0.3 11/1.5 parallel b                                                  1.5 μm Δ ◯       d  12/0.3 12/0.3 perpendicular  X X                                        __________________________________________________________________________

As shown in Table 19, the test pieces a of Nos. 1 to 5 had precipitatesand/or deposits having an average diameter of 10 μm or less and beingarranged in parallel with the largest surface thereof. The test pieces bof Nos. 1 to 5 had precipitates and/or deposits having an averagediameter of 10 μm or less and being arranged in perpendicular to thelargest surface thereof. The test pieces c of Nos. 1 to 5 hadprecipitates and/or deposits either of which had an average diameter ofmore than 10 μm, but both of which were arranged in parallel with thelargest surface thereof. All of the test pieces a to d of Nos. 1 to 5exhibited the excellent resistance to gas corrosion and plasma. Contraryto this, the test pieces d of Nos. 1 to 5, corresponding to thecomparative examples and not satisfying the conditions of the presentinvention, exhibited the insufficient resistance to gas corrosion and/orplasma.

INDUSTRIAL APPLICABILITY

As has been described above, the first and second inventions provide avacuum chamber made of aluminum or its alloy having remarkably enhancedresistance to gas corrosion and plasma, and a surface treatment methodfor the vacuum chamber. The third invention provides the aluminum alloymaterial for the vacuum chamber to achieve excellent resistance to gascorrosion and plasma.

What is claimed is:
 1. A vacuum chamber or chamber part made of aluminumor aluminum alloys comprising an anodic oxide coating including a porouslayer having a number of pores and a barrier layer without pores, thepores having an opening on a surface of the chamber or chamber part, thediameter of the pore being smaller at a top thereof than at a bottomthereof.
 2. A vacuum chamber or chamber part made of aluminum oraluminum alloys according to claim 1, wherein the pore in the porouslayer has a section in a depth direction thereof where its diametercontinuously changes.
 3. A vacuum chamber or chamber part made ofaluminum or aluminum alloys according to claim 1, wherein the pore inthe porous layer has a section in a depth direction thereof where itsdiameter discontinuously changes.
 4. A vacuum chamber or chamber partmade of aluminum or aluminum alloys according to claim 2 or 3, whereinthe pore in the porous layer has a section in a depth direction thereofwhere its diameter remains constant.
 5. A vacuum chamber or chamber partmade of aluminum or its alloys according to any one of claims 1 to 3,wherein the anodic oxide coating contains two or more elements selectedfrom a group consisting of carbon, sulfur, nitrogen, phosphorus,fluorine and boron.
 6. A vacuum chamber or chamber part made of aluminumor aluminum alloys according to any one of claims 1 to 3, wherein a basematerial contains particles of precipitates and/or deposits having adiameter of 10 μm or less in average.
 7. A vacuum chamber or chamberpart made of aluminum or its alloys according to any of claims 1 to 3,wherein the particles of precipitates and/or deposits are arranged inparallel with a largest surface of the base material.
 8. A vacuumchamber or chamber part made of aluminum or its alloys according to anyof claims 1 to 3, wherein the base material contains the particles ofprecipitates and/or deposits having a diameter of 10 μm or less inaverage, and the precipitates and/or deposits are arranged in parallelwith a largest surface of the base material.
 9. A vacuum chamber orchamber part made of aluminum or aluminum alloys according to claim 1,wherein the pore diameter at the top is 80 nm or less.
 10. A vacuumchamber or chamber part made of aluminum or aluminum alloys according toclaim 1, wherein the pore diameter at the top is 50 nm or less.
 11. Avacuum chamber or chamber part made of aluminum or aluminum alloysaccording to claim 1, wherein the pore diameter at the top is 30 nm orless.
 12. A vacuum chambers or chamber part made of aluminum or aluminumalloys according to claim 1, wherein the thickness of the anodic oxidecoating is 0.05 μm or more.
 13. A vacuum chambers or chamber part madeof aluminum or aluminum alloys according to claim 1, wherein thethickness of the anodic oxide coating is 0.01 μm or more.
 14. A vacuumchambers or chamber part made of aluminum or aluminum alloys accordingto claim 1, wherein the thickness of the anodic oxide coating is 0.05 to50 μm.
 15. A vacuum chambers or chamber part made of aluminum oraluminum alloys according to claim 1, wherein the thickness of theanodic oxide coating is 0.1 to 50 μm.
 16. A vacuum chambers or chamberpart made of aluminum or aluminum alloys according to claim 1, whereinthe thickness of the barrier layer is 50 μm or more.
 17. A vacuumchambers or chamber part made of aluminum or aluminum alloys accordingto claim 1, wherein the thickness of the barrier layer is 80 μm or more.18. A method for anodizing a surface of a vacuum chamber made ofaluminum or aluminum alloys, wherein a final anodizing voltage is set tobe higher than an initial anodizing voltage.
 19. A method according toclaim 18, wherein the anodizing voltage is continuously changed for anarbitrary period.
 20. A method according to claim 18, wherein theanodizing voltage is discontinuously changed for an arbitrary period.21. A method according to claim 19 or 20, wherein the anodizing voltageis kept constant for an arbitrary period.
 22. A method according to anyone of claims 18 to 20, wherein the initial anodizing voltage is 50V orless.
 23. A method according to any one of claims 18 to 20, wherein thefinal anodizing voltage is 30V or more.
 24. A method according to anyone of claims 18 to 20, wherein an oxalic acid solution is used as ananodizing solution 1 gram or more of oxalic acid being contained per 1liter of solution.
 25. A method according to claim 24, wherein one ormore elements selected from a group consisting of sulfur, nitrogen,phosphorus, fluorine and boron are added to the anodizing solution. 26.A method for anodizing a vacuum chamber and chamber parts made ofaluminum or aluminum alloys to form an anodic oxide coating including aporous layer having a number of pores and a barrier layer having nopores, the method comprises a step of performing a porous anodizing anda step of performing a non-porous anodizing, and the non-porousanodizing is performed after the completion of the porous anodizing. 27.A surface treatment for a vacuum chamber and chamber parts made ofaluminum or aluminum alloys according to claim 26, wherein a finalporous anodizing voltage is set to be higher than an initial porousanodizing voltage.
 28. A surface treatment for a vacuum chamber andchamber parts made of aluminum or aluminum alloys according to claim 26or 27, wherein a porous anodizing voltage is continuously changed for anarbitrary period.
 29. A surface treatment for a vacuum chamber andchamber parts made of aluminum or aluminum alloys according to claim 27,wherein a porous anodizing voltage is discontinuously changed for anarbitrary period.
 30. A surface treatment for a vacuum chamber andchamber parts made of aluminum or aluminum alloys according to claim 27,wherein a porous anodizing voltage is continuously changed for anarbitrary period in the entire porous anodizing process, and isdiscontinuously changed for the other arbitrary period.
 31. A surfacetreatment for a vacuum chamber and chamber parts made of aluminum oraluminum alloys according to any one of claims 26, 27, 29 and 30,wherein the initial porous anodizing voltage is 50V or less.
 32. Asurface treatment for a vacuum chamber and chamber parts made ofaluminum or aluminum alloys according to any one of claims 26, 27, 29and 30, wherein the final porous anodizing voltage is 30V or more.
 33. Amaterial used for manufacturing a vacuum chamber and chamber parts madeof an aluminum alloy comprising precipitates and/or deposits having adiameter of 10 μm or less in average, thereby giving excellentresistance to gas corrosion and plasma.
 34. A material used formanufacturing a vacuum chamber and chamber parts made of an aluminumalloy comprising precipitates and/or deposits arranged in parallel witha largest surface of the base, thereby giving excellent resistance togas, corrosion and plasma.
 35. A material used for manufacturing avacuum chamber and chamber parts made of aluminum alloy comprisingprecipitates and/or deposits have a diameter of 10 μm or less inaverage, and at the same time, the precipitates and/or deposits arrangedin parallel with a largest surface of the base, thereby giving excellentresistance to gas, corrosion and plasma.
 36. A material used formanufacturing a vacuum chamber and chamber parts according to any one ofclaims 33 to 35, wherein the volumetric proportion of the precipitatesand/or the deposits is 2% or less.
 37. A material used for manufacturinga vacuum chamber and chamber parts according to any one of claims 33 to35, wherein said precipitates and/or deposits comprise at least one ofmagnesium, silicon, copper or iron.